Bottlehead Forum

Bottlehead Kits => Stereomour II => Topic started by: Sugar Man on October 16, 2018, 06:38:29 AM

Title: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Sugar Man on October 16, 2018, 06:38:29 AM
Has anyone tried this yet? If so, how'd did it go? If not, is this still the latest thinking?

I'll have another crack at this, the list is kind of long:

1.  The 3K resistor in parallel with each 2K resistor should be removed and replaced by an 8.2K resistor (a Vishay PR-03 will probably fit OK).  This adjusts the cathode bias voltage.

2.  The 130R/3W resistors in the power supply need to be removed and replaced with 600 ohm 5W resistors.  It may be easier to just replace the two resistors that go from the 5 lug strip by the power transformer to the other two 5 lug strips with 1.1K/10W resistors and leave the other two 130 ohm resistors where they are.  Your mileage may vary, let us know which way works best.  This change lowers the power supply voltage for the 45.

3.  The 0.15 ohm resistors need to be removed and replaced with 0.22 ohm 2W resistors (3W is fine too).  This will reduce the filament voltage to 2.5V when the 45 is plugged in (the 2A3 draws more current, so if you don't change the resistors the filament voltage will be too high).

4.  The black wire from each plate choke needs to be disconnected from the power supply and the red wire connected in its place.  This sets the plate choke to the higher inductance/lower current setting for the 45.

5.  The parallel feed capacitor should be increased to a 5uF/630V part (4.7uF is totally OK).  This works in conjunction with step 4.

The presence of the DC filament upgrade will change the value of those 0.22 ohm resistors.  If someone can report what filament voltage they are getting (DC voltage between pins 1/4) with the 45 and the DC filament supply, we can suggest  tweaks to those values.

I think this is everything.  If anybody buys the parts and performs the steps, let us know and we can direct you to some voltage measurements to check that things are operating properly.

I would also note that the shunt regulated driver stage might call for tweaking the power supply dropping resistors a little bit as well.  It may be that a pair of 1K/10W resistors and 2 of the 4 original 130R resistors might be a better combo in the power supply.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on October 16, 2018, 07:11:02 AM
I think there's still time for someone to be the first.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Jamier on October 16, 2018, 08:09:00 AM
I remember that Greg (gstitt) was working on it last year. You might ask him. Check his posts on page 3.

Jamie
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Sugar Man on October 17, 2018, 06:20:20 AM
I think there's still time for someone to be the first.

I think I'll give it a shot, but I will definitely need some help from the experts.  8)

I will even try to resist the urge to start with boutique tubes and capacitors. Solens for the capacitors? Any recommendations for reasonably priced 45's?
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on October 17, 2018, 06:22:56 AM
Yeah, keep it simple for now.  A used pair of 45s on eBay isn't going to be particularly expensive (once everything is working as it should, then consider the fancy new production stuff).
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: 2wo on October 17, 2018, 01:51:35 PM
If you have any kind of tube friendly speakers, the 45 can be pure magic.

 My SR-45 is still my number one amp by a long margin...John
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Alby0521 on October 17, 2018, 05:57:00 PM
Hi all.

Is the quote of the 1st post the most recent ‘’guide’’ To convert Stereomour II into 45?
If I follow those instruction I’ll be able to run 45 on it?

Does anybody know what the correct reading of resistance and V I should have once I do the change?

I’ve been looking to do this change since a while but never got to it. Maybe this is the right time.

Thanks in advance.

Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Joppa on October 17, 2018, 07:50:53 PM
We have not actually done it ourselves, so we can't say with confidence what the voltages will be. I can calculate expected voltages at the tube pins, but detailed resistances and voltages really must be measured on a working sample if they are to be believable.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Jamier on October 19, 2018, 05:06:21 PM
If you have any kind of tube friendly speakers, the 45 can be pure magic.

 My SR-45 is still my number one amp by a long margin...John

John, I remember that you said you listen to speakers with sensitivities in the mid 80's in conjunction with your 45 amp(s). Do you listen near field or in a larger area? The 45 version of the SII is something I have wanted to try for a while. I'm trying to get a handle on what to expect from 1.75 watts in a nearfield environment.I have 92db sens MTMS that I use with the 2A3 version and they play plenty loud.

Jamie
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 20, 2018, 05:21:19 AM
I haven't found a post on it, so I'll add this to the mix: EML has a new "45B" tube that can deliver twice the output power of a regular 45. It can be found at jacmusic.com under Tubes/Products/ (the website architecture isn't entirely intuitive).  I don't have the technical knowledge to determine whether this tube would work with the SII, but the promise of a Stereomour 45 with no loss of power sure is appealing!

Here are the basic specs from the website:

EML 45B  Filament Ratings
Filament Voltage    
= 2.5Volt (AC or DC)
Tolerance on filament voltage   
5%
Filament Current    
~ 1.5Ampere
.
EML 45B Maximum Conditions
Plate Voltage    
420Volt
Plate Current    
53mA
Minimum Plate Dissipation   
8.5Watt
Continuous Plate Dissipation   
22Watt
Power Output in Class A    
5.2Watt
Grid resistor   
500k Ohm

 
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on October 20, 2018, 05:47:37 AM
I haven't found a post on it, so I'll add this to the mix: EML has a new "45B" tube that can deliver twice the output power of a regular 45.
Continuous Plate Dissipation   
22Watt
Power Output in Class A    
5.2Watt
This will potentially put out more power than a 2A3, but you'll need a different power transformer with a much higher voltage winding. (Think the Kaiju HV supply and Stereomour LV supply)

You'll end up with an amp that will only work for the EML 45B.

It does look like the 45B would plug into a 45 modded Stereomour I/II and work just like a 45, but you aren't going to get any extra power.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 20, 2018, 07:04:34 AM
Bummer. So is the drop in power output going from a 2A3 (3.5W) to a 45 (1.75W) because the 45 is half as efficient as the 2A3? And therefore, in an SII, you'll never get more than 1.75 Wpc from a 45, regardless of how much power the 45 can handle?
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on October 20, 2018, 07:11:17 AM
The 2A3's plate can dissipate 15W, while the 45 can dissipate about 10W.  The filament of the 2A3 is also substantially beefier than the 45.  It isn't a matter of efficiency so much as physical size and capabilities of each device. 
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 20, 2018, 07:23:53 AM
Thanks PB
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Jamier on October 20, 2018, 07:52:22 AM
PB, The EML website says that their 45s can have center tapped filaments(?) Can the SII be modified to use this version of the tube?

Jamie
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on October 20, 2018, 08:51:17 AM
The center tapped tube is going to have a different base, so a different socket will be required.  This will further push the amp to a state where it can only take one tube. 

IMO, the center tapped tube idea is solving a problem that isn't really there.  A lot of what's written about the center tapped tubes is in regards to reducing hum.  Do you need to reduce hum in your amp?

While it would be nice for the cathode bypass cap/resistor to connect to the filament center tap directly, we add about 13R between the cathode resistor/bypass cap and the filament, which isn't a particularly performance altering amount of resistance in this context.  I have seen a great many schematics that just throw a 100 ohm hum pot in and call it good. 
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: 2wo on October 20, 2018, 06:05:55 PM
Jamier, My room is about 16x25 so I don't listen near feild and have a verity of speakers.
 If you are running 2A3's and don't think you are pushing them to the limit I bet the 45 will work for you...John
Title: Conversion to 45s Questions
Post by: Deke609 on November 22, 2018, 12:26:11 PM
I hope to be able to figure this out myself one day not too far in the future, but right now I need the input of BH experts: is conversion to 45s compatible with the Shunt reg upgrade and the DC Filament upgrade?  I am fine with having to change the values of some/all the components on the boards.

I ask b/c I'm considering getting another SII and converting both it and my existing one to run as 45 monoblocks, which combined would give me about the same output power as my existing SII 2A3 (maybe even a bit more?).  But I also want to keep benefits of the SR and DCF upgrades b/c they are amazing.

I am perfectly ok with the conversion and tweaking taking a long time or lots of experimentation (with BH guidance I hope).

If it's doable, I'd like to take advantage of the Gray Thursday sale and get the new SII before BH switches to the new periodic availability sales system in the coming year.

cheers and thanks,

Derek


Title: Re: Conversion to 45s Questions
Post by: Paul Birkeland on November 22, 2018, 01:48:41 PM
I hope to be able to figure this out myself one day not too far in the future, but right now I need the input of BH experts: is conversion to 45s compatible with the Shunt reg upgrade and the DC Filament upgrade?
The resistors that get changed on the 4 pin sockets will allow both the AC and DC filament supplies to work properly with 45s, but no longer 2A3s.

I ask b/c I'm considering getting another SII and converting both it and my existing one to run as 45 monoblocks, which combined would give me about the same output power as my existing SII 2A3 (maybe even a bit more?).  But I also want to keep benefits of the SR and DCF upgrades b/c they are amazing.

That's a fun idea, but I'd say convert one to 45s and compare it against the 2A3 version.  There's lots to be learned there.  We'll be here to help you with the 45 conversion when you're ready to do it.

I'd also consider the Kaiju...
Title: Re: Conversion to 45s Questions
Post by: Deke609 on November 22, 2018, 02:07:42 PM
The resistors that get changed on the 4 pin sockets will allow both the AC and DC filament supplies to work properly with 45s, but no longer 2A3s.

Many thanks again PB. So just to confirm: the DCF will work, but what about the Shunt regulation upgrade? I assume it will, but want to be sure b/c for me it is the best of the 3 upgrades.

I'd have to see what's involved in changing the resistors to the sockets, but it sounds like a small switch board could be devised to allow switching back and forth between 2A3 and 45 - even if it would require a ton of switches, it would be worth doing.

Quote
I'd also consider the Kaiju...

Yeah, I've been thinking about getting a Kaiju for a while. The dual S45 setup would be instead of getting a Kaiju (at least temporarily  :D). 2 considerations push me in favor of dual S45s: (1) I already have an SII and don't want it sidelined by the Kaiju - I like it too much to sell it, but if the Kaiju is "better" the SII will just sadly sit on an upper shelf; and (2) everything I've read about 45 amps make me think they'll be right up my alley.

Edit: and yeah, I agree that it makes sense to convert one to 45 to compare 45 and 2A3 before proceeding to dual 45 monoblocks.  that was my thinking.
Title: Re: Conversion to 45s Questions
Post by: Paul Birkeland on November 22, 2018, 04:23:26 PM
Many thanks again PB. So just to confirm: the DCF will work, but what about the Shunt regulation upgrade? I assume it will, but want to be sure b/c for me it is the best of the 3 upgrades.
The shunt reg upgrade won't be affected.  The available B+ voltage for the SR upgrade will drop a little, but not enough to prevent proper operation.


I'd have to see what's involved in changing the resistors to the sockets, but it sounds like a small switch board could be devised to allow switching back and forth between 2A3 and 45 - even if it would require a ton of switches, it would be worth doing.
No, absolutely not.  This is a terrible idea that is likely to destroy many of your tubes and potentially damage your amplifier. 

Title: Re: Conversion to 45s Questions
Post by: Deke609 on November 22, 2018, 04:56:54 PM
No, absolutely not.  This is a terrible idea that is likely to destroy many of your tubes and potentially damage your amplifier.

Because it can't work, or because I'll inevitably mis-set the switches and put too much / too little into the tubes?
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on November 22, 2018, 06:12:17 PM
You don't want to have a toggle switch sitting at 400V DC, and you'll need more than one to do what you're talking about. 

You will switch the filament switch to "2A3" while running a 45 and damage the 45.  You will switch the filament switch to "45" while running a 2A3 and damage the 2A3.  The same goes for the HV/cathode bias resistor switches, as running the 45 under 2A3 conditions will roast the 45. 

More than a decade ago I had an amp that wasn't too dissimilar to this and I destroyed plenty of tubes.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on November 23, 2018, 02:02:58 AM
Thanks PB. So the problem is human idiocy - I have plenty of that, so my interest in the switch is now lessened (but not gone). Were I to install a switching setup, I'd have the switches under the chassis so that I'd have to power down, remove the tubes and flip the chassis over to change between tube types. It would also be interesting to incorporate color-coded leds to indicate on the top of the chassis how the amp set. I'd have to look at the circuit, but I would think a loop off of the high VDC supply with a very high value resistor and led might work, with some possible tweaking to the R value of the resistor that goes to the tube to take into account the new resistor/led loop.

But I've decided to wait until next spring before getting a new S2 and converting to 45s.  I have enough to keep me busy until then.  My BeePre just shipped and I have a Quickie and Quicksand on order. And I haven't even started experimenting with the Nickel Wonder yet. So lots of fun stuff to do. The BeePre will take a long time to build - I plan to shield every bit of signal wire that I feasibly can with copper tubing or braid - which in almost all places will mean adding a color-coded insulating layer over top of the braid to prevent shorts. And wiring all the shielding to ground. It is going to take forever - which is awesome b/c after the thrill of completing a project wears off (usually in a day) I am always disappointed that I no longer have something to work on.

cheers,

Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on November 23, 2018, 01:47:47 PM
Well, curiosity got the better of me and I ordered a new S2, which I will build as 45 when it arrives.

Question: since I will likely convert my existing S2 and the new one to monoblocks sometime later next year, will I need a matching quad of 45s? I hope not b/c that could be hard to find, or very expensive.  Can I just get two matching pairs (AA and BB), and install one tube from each pair (AB) in each amp - thereby equalizing the two amps?

If I can split the pairs between amps, I can get a matching pair now for the initial 45 build and then another matching pair later when I convert the existing S2.

2nd Question: does anyone have any thoughts on what 45s I should look to get?  And from where?  They seem to be pretty rare.

cheers and many thanks,

Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on November 24, 2018, 06:34:01 AM
These are all experiments that you can do when you have both amps setup.  There aren't a whole ton of variations of vintage 45s, so finding a construction matched quad shouldn't be too tough.  An electrically matched quad of 45s is not necessary.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on November 24, 2018, 07:02:42 AM
Thanks PB.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: maryc27182 on November 24, 2018, 05:36:48 PM

2nd Question: does anyone have any thoughts on what 45s I should look to get?  And from where?  They seem to be pretty rare.


For the ST types, I like the Sylvania's that have the two wire mica supports that touch the glass (those are found under other brand names as well--just look for that same structure.) Unfortunately for my wallet, like many others, I found the globe 45s really compelling. I currently use RCA globes (Radiotron with triangular-ish mica). It was much more difficult to find good-testing, not-noisy globes for reasonable amounts of cash.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on November 25, 2018, 02:19:52 AM
Many thanks, Mary.

From what I've come across online, the globes appear to be universally preferred. But they are pricey!  And the prices of the new production 45s from Emission Labs are astronomical. 

Regarding the Sylvania ST tubes, are the mica supports plainly visible in a photo of the tube? If not, do the tubes have any distinctive branding? I ask b/c the larger vendors of NOS rarely provide photos of each tube, and when they do the photos are not very detailed.

cheers and thanks,

Derek

Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: maryc27182 on November 25, 2018, 06:02:14 AM
The mica is almost oval shaped (imagine a circle and someone has put straight cuts on two sides)--some of the Sylvania's have a more complicated mica shape, and those don't have the two wire supports. I've also seen these branded as Zenith, Philco and Ken-Rad. Let me know if the photo gives you enough info. --Mary
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: maryc27182 on November 25, 2018, 06:07:50 AM
Also, tip of the hat to this thread which helped me when I was looking for 45s: https://www.diyaudio.com/forums/tubes-valves/120611-hashimoto-wonderful-45-a.html (https://www.diyaudio.com/forums/tubes-valves/120611-hashimoto-wonderful-45-a.html)
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on November 25, 2018, 06:12:46 AM
Thanks so much, Mary. That's really helpful.  I'm guessing those supports help cut down on vibration/microphonics.  I will keep my eye out for similarly constructed tubes.

cheers,

Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 07, 2019, 04:45:31 PM
 I decided to go with a pair of the EML 45B's.  My second SII kit has shipped from BH and should arrive shortly.

I no longer plan to build dual 45 Stereomour monoblocks - at least not this year. For now I will keep one SII as a 2A3 and the other as a 45, modded to take full advantage of the 45B tube's higher power output capacity.

Order of operations:

(1) Get new SII up and running in stock 2A3 configuration with all 3 upgrades - albeit with a larger chassis to accommodate bigger iron in the future. I'm thinking a 12" x 12" copper chassis. Or maybe even 14 x 14.

(2) Convert to standard 45, burn in and compare with the 2A3 version.  The EML 45B's are stated to be compatible with standard 45 amps.

(3) Replace the PT, OTs and chokes and make other necessary modifications to run the 45Bs to get somewhere between 3.5 and 4.5 wpc. Since Kaiju iron is not available, I am leaning towards Lundahl transformers and chokes.  The EML webpage for the 45B has some recommended operating points for various Lundahl OTs: http://www.emissionlabs.com/datasheets/EML45B.htm (http://www.emissionlabs.com/datasheets/EML45B.htm)  It looks like I have 3 options that will give me my desired output wattage.

I welcome any thoughts/input on which iron to go with. The amp will be used with my Audeze LCD4 headphones. On my current SII 2A3 I listen with the OT's configured for 16 Ohms. Damping really isn't a factor b/c the LCD4 has  200 Ohm input impedance and completely flat plot of impedance against frequency.  And they like a lot of power.  One of the main things I'm looking for with the 45 conversion is greater bass extension. 

The biggest question I have is whether the SR upgrade and the DCF upgrade can be modded to work with the 45B amp at the wattages I want. PB indicated that the SR and DCF will work with a standard 45 amp, but what about at double the standard wattage output? Is this doable? It would be great if I could use the BH boards and only need to swap out some components.  I hope to use the build as an opportunity to learn more about how these circuits actually operate. I learned some of the basics building a "Nickel Wonder" preamp that PB suggested - which I realize is incredibly simple in comparison to an SII.  I think the prospect of having a powerful 45B SII amp will motivate me to take my learning up a notch. But any guidance that BH can provide on the build will be most appreciated!  :)

Of course, one suggestion might be to just get a Kaiju. I hope to do so later in the year, but will pair the Kaiju with Jaegers. 

cheers and many thanks in advance,

Derek





Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Doc B. on January 07, 2019, 05:10:35 PM
Quote
I welcome any thoughts/input on which iron to go with.

Sure, since you plan on a bigger chassis the all nickel MQ EXO-050s I have for sale will rock with 45s. Look for plate chokes in the 50H range to go with them.

https://bottlehead.com/smf/index.php?topic=11296.0 (https://bottlehead.com/smf/index.php?topic=11296.0)
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on January 07, 2019, 05:48:59 PM
(1) Get new SII up and running in stock 2A3 configuration with all 3 upgrades - albeit with a larger chassis to accommodate bigger iron in the future. I'm thinking a 12" x 12" copper chassis. Or maybe even 14 x 14.
The 12x12 is probably just enough extra room. 

(3) Replace the PT
This would be a really, really bad idea.  You can basically throw away the DC filament supply, SR driver supply, and stock power supply.  If you go any get something from Hammond, it will probably hum and annoy you.  Then you'll have to figure everything else out from scratch.  While we are normally very helpful on this forum, if you need help we will just tell you to put the stock transformer back in.

OTs and chokes and make other necessary modifications to run the 45Bs to get somewhere between 3.5 and 4.5 wpc.
Well, if you want to do that, you are probably better off with a Kaiju and Doc B's 5K nickel output transformers, then add an appropriate filament transformer to heat the EML tubes.


The amp will be used with my Audeze LCD4 headphones. On my current SII 2A3 I listen with the OT's configured for 16 Ohms. Damping really isn't a factor b/c the LCD4 has  200 Ohm input impedance and completely flat plot of impedance against frequency.  And they like a lot of power.  One of the main things I'm looking for with the 45 conversion is greater bass extension. 
I would just go with the normal 45.  The extra power will be barely audible, and seems a little silly on headphones. 

The biggest question I have is whether the SR upgrade and the DCF upgrade can be modded to work with the 45B amp at the wattages I want. PB indicated that the SR and DCF will work with a standard 45 amp, but what about at double the standard wattage output?
The driver and DC filament supply won't care about that, but when you toss the power transformer, you kind of have to toss the rest of the amp.

Is this doable? It would be great if I could use the BH boards and only need to swap out some components.  I hope to use the build as an opportunity to learn more about how these circuits actually operate. I learned some of the basics building a "Nickel Wonder" preamp that PB suggested - which I realize is incredibly simple in comparison to an SII.  I think the prospect of having a powerful 45B SII amp will motivate me to take my learning up a notch. But any guidance that BH can provide on the build will be most appreciated!  :)
I do understand what you're after, and I can tell you (from experience) that the amount of fine tuning that we had to do to get the DC filament supply on the Stereomour II to work properly was a little crazy.  There is no other power transformer from any other manufacturer that I have seen that will give you the AC voltage you need to get that module to work. 

Of course, one suggestion might be to just get a Kaiju. I hope to do so later in the year, but will pair the Kaiju with Jaegers. 
Yes, a Kaiju with the DC filament board (which is regulated, and a fair improvement over the design in the SMR2) would be the way to go.  You'll also be able to use lots of different 300Bs from various manufacturers. 
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 07, 2019, 07:49:57 PM
Hmm. Looks like I jumped the gun in getting the 45Bs. I had naively assumed that everything in the SII could simply be "scaled up" to accommodate the greater power output.

But there's still hope that the conversion to 45s will work with the LCD4. I got a good bump in perceived loudness when I added the BeePre in front of my SII . Even when really rocking out, I have the coarse attenuator set at -9dB on the SII with the BeePre fully open.  If I understand this right, every doubling of power yields about a 3dB increase in volume.  So going from 3.5Wpc with the 2A3 config to 2Wpc with 45 should result in less than a 3 dB drop in volume?  Do I have that right?  If so, I think that should be ok - but it will mean running the SII a little closer to fully open.  On the upside, the 45Bs should last forever if only asked to put out 2W.

cheers and thanks,

Derek

Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 08, 2019, 03:59:02 AM
@PB - What about keeping the PT and OTs, but swapping in different after-market plate chokes?  In a different thread, PJ indicated that the PC together with the parafeed cap sets the bass extension.  If the OT-2 is only asked to handle a max of 2W with the 45 instead of 3.5W with the 2A3, I think it follows that the OT-2 should go lower in the bass before saturating - and I am guessing that this is where the greater bass extension comes from with the conversion to 45s.  Could swapping in some after-market PCs push the bass extension even further? In the same thread, you indicated that you had experimented with putting the Kaiju PCs in a Stereomour and were only down -2dB at 8Hz.

If this would work, can you tell me what specs should I look for in a plate choke?  If there are no stock PC's that fit that bill from Lundahl, Electraprint, etc., maybe I could get them custom made.

Many thanks,

Derek

Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on January 08, 2019, 04:54:53 AM
When you do the 45 conversion, part of that involves connecting the entire winding of the plate choke between the 45 plate and B+, which is 40H instead of the 20H in the 2A3 configuration.  This is not possible with the 2A3 because it draws more current, but the reduced current drawn by the 45 allows this connection.  This change in conjunction with changing the parallel feed capacitor will work to improve the low end frequency response.  The power bandwidth of the OT-2 doesn't seem to be the limiting factor in this situation.  If you want to go for the high power 45B, then the plate current goes back up, and you need the other connection.

The Lundahl LL2743 may work, but it's a little off in terms of the options for the air gap. The Sowter 8985 would be the most appropriate aftermarket choice, but it's 50H/40mA, so you're not gaining much over what we provide. 

It kind of sounds like what you may want to do is build the Stereomour stock, then sort out the mods to get to #45s, then do a scratch build with all aftermarket parts. 
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: braubeat on January 08, 2019, 05:15:10 AM
Electraprint will build custom plate chokes to whatever specs you want. I have purchased several. Jack is very knowledgeable and can advise you about what will work well with different tubes.
My favorite amp is a low power parafeed 845 with Electraprint iron throughout.

Michael
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 08, 2019, 10:25:48 AM
It kind of sounds like what you may want to do is build the Stereomour stock, then sort out the mods to get to #45s, then do a scratch build with all aftermarket parts.

Thanks PB. Yeah, that may be road I will need to take. The problem, of course, is that there's a snowball's chance in hell that I'll be able to build an 45B amp that will sound as good as a Stereomour or Kaiju - even assuming that I learn the ton of stuff I still need to learn to even build a 45B amp from scratch. 

So I'm rethinking things again.

The 2nd Stereomour amp on its way to me presents me with another opportunity: if I build it stock, I can bridge the two SII's giving me 7 Wpc. I'd like to hear what the extra headroom might give me.  Until I added the Beepre, my SII could lose some bass slam on some tracks. Example: Rush's Tom Sawyer. It would start out with slam, but once full instrumentation kicked in, the drums became a bit muted. I thought at first that this might just be the recording, but adding the BeePre disproved that hypothesis. With the BeePre in the system, there is no noticeable loss of slam.  (Although how adding the BeePre achieves this, I haven't the foggiest: I would have thought it impossible to get more out the SII by adding a pre-amp -- if an amp can be likened to a pump with a maximum pressure output, my understanding is that you can't increase that pressure output by adding a "pre-pump"; although I guess a prepump could reduce the amount of work the second pump needs to perform to get up to full pressure -- if so, did adding the BeePre make more current available to the headphones at the same voltage output?).

Bridged SII's will give me a sense of what the dynamics of the Kaiju might be like, and whether I want the added headroom.  If Kaiju (which would also give me added bass extension) is the way to go with the LCD4, I can convert the SII's to standard 45s for a very nice 2 channel system for listening at moderate volumes.  I very much miss having speakers, but living in semi-detached house makes loud-ish listening impossible without disturbing my neighbors. 

cheers,

Derek





 

Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 08, 2019, 10:38:23 AM
Electraprint will build custom plate chokes to whatever specs you want. I have purchased several. Jack is very knowledgeable and can advise you about what will work well with different tubes.
My favorite amp is a low power parafeed 845 with Electraprint iron throughout.

Michael

Many thanks Michael.  Some custom Electraprint plate chokes for twin Stereomour 45s could be a fun and manageable project. It's good to know that you've been happy with their products.

cheers,

Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 09, 2019, 03:36:27 PM
The second SiI arrived today and I've started the assembly. I want to give the new amp a minimum of a month of burn-in before bridging the two amps.

In the meantime, I'd like to convert my original SII to 45 and listen to the EML 45Bs. Do PJ's instructions set out on the 1st page of this thread capture the first steps?

Since I will be placing a parts order with Digi-Key, are there any other values of the quoted components that I should pick up in anticipation of having to make some tweaks? Factoring in shipping costs, it will likely be cheaper for me to order a scattershot range of component values in one go than to make make a series of more targeted orders for fewer components.

Many thanks in advance,

Derek

 
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 10, 2019, 05:33:11 AM
...

2.  The 130R/3W resistors in the power supply need to be removed and replaced with 600 ohm 5W resistors.  It may be easier to just replace the two resistors that go from the 5 lug strip by the power transformer to the other two 5 lug strips with 1.1K/10W resistors and leave the other two 130 ohm resistors where they are.  Your mileage may vary, let us know which way works best.  This change lowers the power supply voltage for the 45.

3.  The 0.15 ohm resistors need to be removed and replaced with 0.22 ohm 2W resistors (3W is fine too).  This will reduce the filament voltage to 2.5V when the 45 is plugged in (the 2A3 draws more current, so if you don't change the resistors the filament voltage will be too high).

...

The presence of the DC filament upgrade will change the value of those 0.22 ohm resistors.  If someone can report what filament voltage they are getting (DC voltage between pins 1/4) with the 45 and the DC filament supply, we can suggest  tweaks to those values.

...

I would also note that the shunt regulated driver stage might call for tweaking the power supply dropping resistors a little bit as well.  It may be that a pair of 1K/10W resistors and 2 of the 4 original 130R resistors might be a better combo in the power supply.

@PB - I have both the DCF and SR upgrades. So I'm thinking my best approach is:

(1) leave in place the two 130Rs that connect 34L/31L and 30L/27L, remove the other two 130Rs and add wire leads to their termination points to make it easier to insert different replacement values (1.1K or 1.0K 10W - any other foreseeably likely values?  E.g., 950 or 900?)

(2) order a range of values for replacing the 0.15 ohm resistors - would 0.18 - 0.25 in 0.1 increments be a safe bet? Or is their some other range you would guesstimate?

Many thanks in advance,

Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on January 10, 2019, 05:52:10 AM
There's no reason to expect the 1.1K value to be a problem, you shouldn't need to try different values.

Since you are going to start with AC heating on this build, the 0.15 ohm resistors in the stock build can go to about 0.25 ohms instead (2W is OK). 

When you get to the DC filament installation (which you should do dead last), you can start by installing the resistors provided, then let us know what DC voltage you see across the filament pins.  When I dialed in the kit design, I was ordering resistors in 0.02 ohm increments. 

-PB
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 10, 2019, 07:18:54 AM
Many thanks PB - and just to clarify: I am converting my existing SII that already has the SR and DCF upgrades installed. Is that problem, or would you suggest building the new kit as a 45 from the start?

My thinking is that I'll get a quicker sense of the 45 sound with my original SII b/c the caps and other components are already burned in. And I believe the EML 45Bs come with a partial factory burn-in.

Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on January 10, 2019, 07:39:30 AM
Ah, that changes things a little then.  I would probably just remove the resistors added on the 4 pin socket during the DCF upgrade and then let us know what DC voltage you have after you've done that. 
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 10, 2019, 08:52:00 AM
Many thanks PB - So just so I have this, I am to:

(1) remove the four 0.13 ohm resistors to cathode pins 1 and 4 added during the DCF upgrade;

(2) leave the 0.15 ohm resistors (for now) on cathode pins 1 and 4;

(3) take DC voltage measurements to determine what R value replaces the 0.15s.

Is that right?

Many thanks,

Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on January 10, 2019, 09:07:23 AM
Yes, and don't be too annoyed if I come back and suggest 3 different resistor values to buy, even with your measurements in hand. 
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: 2wo on January 10, 2019, 09:14:16 AM
 Isn't the point of the 45b  is that it can be run at a significantly higher operating point than a standard 45 looks 420v at 53ma max.  This is close to 2A3  maybe you could try adjusting the cathode resistor might be all you need to start ...John
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Doc B. on January 10, 2019, 10:03:54 AM
We have been developing a 3.5 watt 45 tube too.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on January 10, 2019, 12:32:03 PM
This is close to 2A3  maybe you could try adjusting the cathode resistor might be all you need to start ...John
He'd also have to adjust the filaments a bit too because of the lower current consumption. 
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 10, 2019, 12:44:35 PM
We have been developing a 3.5 watt 45 tube too.

Yeah, that was a common response to the 45B on a lot of threads: the reinvention of the 2A3!  Having not even heard a 45 tube, I am taking a flyer with the 45B. We'll see. Hoping for some of the 45 magic I've read so much about.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Doc B. on January 10, 2019, 12:58:12 PM
My take on this is that if you want to hear a 45, buy an old school RCA 45. If you want to hear a 45B, buy a 45B. And understand that they have been made for different conditions and will most likely sound different because of that. We went through this with all the new production tubes that came out with 300B in their designation back in the late 90s and early 2000s. Most sounded very good but all sounded different, particularly the superhero versions.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 10, 2019, 01:04:27 PM
Isn't the point of the 45b  is that it can be run at a significantly higher operating point than a standard 45 looks 420v at 53ma max.  This is close to 2A3  maybe you could try adjusting the cathode resistor might be all you need to start ...John

He'd also have to adjust the filaments a bit too because of the lower current consumption. 

Are you guys suggesting that there might be a way of operating the 45B for more than 2Wpc in the Stereomour?  I had assumed from PB's posts (quite possibly erroneously) that getting more than 2W from the 45B requires a higher voltage/current combo than the SII iron can provide.

EML provides a number of suggested operating points for the 45B. For 2W output: 275V and 36mA. The next higher suggested operating point is 3.1W via 384V and 41mA, which according to the website is one of the better performing operating points.  I've not found a published curve for the 45B, so I have no idea if there are good operating points between 2 and 3.1 watts.

Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on January 10, 2019, 01:23:29 PM
Are you guys suggesting that there might be a way of operating the 45B for more than 2Wpc in the Stereomour?
Yes, but you were also very interested in using the full 40H from the plate choke, which is not possible when operating under the 2A3 conditions.

A matched pair of old stock #45 tubes can generally be bought on eBay for well under $100.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 10, 2019, 01:42:23 PM
Yes, but you were also very interested in using the full 40H from the plate choke, which is not possible when operating under the 2A3 conditions.

A matched pair of old stock #45 tubes can generally be bought on eBay for well under $100.

Thanks PB. Yes, that's true - I am interested in hearing more low-end, which I take it requires switching from 20H to 40H to get the added bandwith. But I would also be interested in hearing the 45B's with more than 2Wpc just to keep some headroom. If the 3.1W operating point is an easier modification, could you help me with that to start?  And then after a month or more, I could move on the mod outlined in this thread?

many thanks,

Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on January 10, 2019, 03:21:09 PM
PJ would have to comment on how much plate current the choke will take before saturating.  Even the 3.1W operating point may push the entire winding a little too far.  Also, going from 2W to 3.1W isn't quite a 2dB increase in level, so not exactly earth shattering.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 11, 2019, 05:10:08 AM
... going from 2W to 3.1W isn't quite a 2dB increase in level, so not exactly earth shattering.

Thanks PB. Yeah, not a ton of extra headroom, but every little bit helps.  I think a 45B amp at 3.1W would make for a fair comparison with a 2A3 amp at 3.5 - I won't get the bass extension, but the 45B is supposed to have a very nice midrange, and I can listen for that and not need to factor in differences in headroom between the 2A3 and the 45B.  I have in mind 3 different comparisons:

(1) 45B/3.1W vs. 2A3/3.5W - roughly equal headroom

(2) 45B/2W vs. 2A3/3.5W - for whether I like/want the added bandwidth - I may pick up some regular 45s for this as well.

(3) one 2A3/3.5W amp vs. bridged 2A3/7W two-amp combo - for benefits of 3dB of added headroom over my existing single 2A3 amp

Based on the above experiments, I can decide on which configuration/compromise suits me best: bridged pair of 45Bs @ 6.2W (more headroom) or @ 4W (greater bandwidth), or a bridged pair of 2A3s @ 7W.  If greater bandwidth wins the day, I may even consider parting with my LCD4s and looking for a used pair of the LCD4z.  Man, the LCD4s like a lot of juice.  Example: vol. pot settings listening to Rush's Tom Sawyer at the perceived same loudish volume level: LCD4 @ -6dB vs. Focal Elex @ -24dB.  And that's with the BeePree fully open. at -9db. With the BeePre fully open, I turn the SII down to -18dB on the LCD4s, but I hear what sounds to me like a bit of distortion or auditory halo around notes (which works quite well with the bloozy rock I often listen to)

I should clarify again, for others that who might read this, that I am not trying to solve a perceived performance problem. My BeePre/Stereomour II combo is absolutely killer with my LCD4s. IMHO, anyone with headphones that are hard or moderately difficult to drive should consider the SII w/ the DC Filament upgrade (but I recommend getting the other 2 as well - the Shunt Regulation upgrade is particularly amazing).

cheers,

Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Joppa on January 11, 2019, 10:00:28 AM
PJ would have to comment on how much plate current the choke will take before saturating.  Even the 3.1W operating point may push the entire winding a little too far.  Also, going from 2W to 3.1W isn't quite a 2dB increase in level, so not exactly earth shattering.
My measurements indicate 45mA as the limit for the two chokes I measured. I have been rating the PC-3 as 40mADC (full winding), which is a little conservative and allows for some variation in manfacturing.

Using the 45B, you could probably not change the high-voltage power supply - just make the other changes. You might see 310v or 320v plate to cathode, rather than 275v. With the 1600 ohm cathode resistance, I estimate 41mA would be drawn, and you might get 2.6 watts output. Plate dissipation about 13 watts - don't try this with a standard 45!

For a little perspective, I note that the EML operating points are higher voltage without much higher current; consequently they are optimized for much higher impedance output transformers (6500 or 9200 ohms, vs. 4000 for Stereomour). While I agree this is a good idea, it is not usually done with the standard 45, which is limited to 275v maximum plate to cathode.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 11, 2019, 01:21:04 PM
Many thanks PJ.

So initial steps for the 2W+ conversion for EML 45B tubes are (please correct me if I'm wrong):

(1) Replace the 3K cathode bias resistors in parallel with the 2Ks with 8.2Ks to get 1.6K combined;

(2) Leave the 130R resistors in the power supply alone.

(3) Remove the 0.13 ohm resistors that are in parallel with 0.15 ohm heater resistors.

(4) Connect red wire of plate chokes in place of black wire - do I simply insulate the exposed end of the black wire and leave it disconnected?

(5) Swap in 5uF or so 630V parafeed caps.

(6) Measure DC heater voltages and report back for tweaking the heater resistor values.


Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Joppa on January 11, 2019, 02:11:11 PM
In the stock 2A3 build, the red wire of the PC-3 plate choke dead-ends at T2 and T19. You should be able to unsolder the red and replace it with the black, connecting the reds to 27 and 34 (where the black was originally).

The above instruction is based on the manual and my memory, so I can't be certain I have it entirely right - but that was my design intent!
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Jamier on January 11, 2019, 03:55:42 PM
In my builds I cut the black wire excess off before connecting to the PS so my blacks will no longer reach 2 and 19. I guess I can just terminate them with shrink (?).

Jamie
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 11, 2019, 04:01:00 PM
@PJ - many thanks. So just swap terminations of black and red.

@Jamie - you've done the conversion to 45? What are your impressions? You mention "builds" (plural) - have you converted two amps?  And do you have the DCF upgrade? If so, what if any tweaks did it need?

cheers,

Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Jamier on January 11, 2019, 04:22:52 PM
No,  I have built 3, 2A3 versions, one with the PS caps swapped for PP films. The other two are stock and series bridged to get the 7WPC. I am thinking of converting one of the stock amps to 45s and if I like it I will convert the other and series bridge again to get the 3.5 WPC, 45. The series bridged 2A3 amps are good, but I listen nearfield in a small room and I find that I really don't need the power. What I want is an even better 3.5 WPC. That is enough power in my small space at the levels that I listen at. I think this is going to be great!

Jamie
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 11, 2019, 06:41:32 PM
Ah, gotcha, I misread your reference to cutting the black wires to mean you cut them while doing the conversion.

3 Stereomours - nice!

Re bridging the two amps: I am thinking along exactly the same lines. Please share your impression when you get the first 45 up and running.

cheers,

Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 15, 2019, 12:55:14 PM
@PB - I made the required changes (swapped 8.2Ks for the 3Ks, removed the 0.13 Ohm DC heater resistors, swapped 4.7 uf for 3.3 uF caps, and swapped  red and black PC wires).

With the 45Bs, I measure 2.53 to 2.55 V (seems to oscillate up/down between the range values) between pins 1 and 4 of both tubes.  At first, I measured 2.50V, but that value slowly climbed until settling in at the aforementioned range.

Edit: the EML 45B filament is rated for 2.5V with a 5% tolerance. So it looks like I'm within spec. But I don't know whether the filament heater volatage would have continued to slowly climb - I only had the meter leads on for about 3-5 min.

What's next? I bought a whole bunch of 3W resistors for tweaking the heater R values.

cheers and thanks,

Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on January 15, 2019, 01:07:43 PM

With the 45Bs, I measure 2.53 to 2.55 V (seems to oscillate up/down between the range values) between pins 1 and 4 of both tubes.
Yeah, you won't need any of those resistors.  That's a great voltage to get! 
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 15, 2019, 01:09:51 PM
Awesome. Thanks PB. Gonna give it a listen!
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 15, 2019, 02:36:37 PM
Well ... I screwed that up nicely.

I mistakenly ordered and installed 8R2 instead of 8K2 5W resistors!!!! So, instead of 1600 Ohms, I had 8.2 Ohms. Sweet Marie!   :'(

I am praying I haven't fried anything (there was no smoke and no popping).

It sounded terrible .. very distorted, like the tubes were being pushed way too hard. Stupidly I gave it some time (about 20 - 30 min) and then finally turned the amp off, convinced that something wasn't right. And then I checked the mods I made to the power supply ... and there it was: "8R2" ... awh crap.

Have ordered 8K2 5W. Amp will stay off until I install them.

How likely is it that I've damaged the amp?
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on January 15, 2019, 03:07:23 PM
Try running the amp with the 2K cathode resistors and do a voltage check.

The likely things that will be destroyed will be the tubes and/or the plate chokes. 

Always check your voltages after powering up.  I'm sure you would've found that all the HV voltages were extremely low.  Luckily that extra power supply resistance you added probably took the brunt of the abuse. (and your 45s)
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 15, 2019, 03:23:51 PM
So, remove the 8R2s, and run the voltage checks with the 45Bs?
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on January 15, 2019, 03:38:19 PM
Yes.

Running experimental tests with a $649 pair of tubes doesn't seem like the best choice when inexpensive used 45s are floating around all over eBay.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 15, 2019, 04:37:07 PM
Voltages with 2K cathode resistor and 45Bs:

1-   367.5 to 368.5
2-   391-392
6-   63.4
7-   189.5
14-  191.8
15-  63.4
19-  390
20-  371
21-  63.6
22-  65.2
24-  61.8
25-  63.1
27-  396
30-  400-402
31-  402
34-  397
36-  63.2
37-  62.3
39-  65.3
40-  63.2

Many thanks PB.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Joppa on January 15, 2019, 04:52:57 PM
The error will have produced excessive cathode current, which might have damaged the filament coating of the 45Bs. However, if that happened, sometimes it can be restored, so don't panic! Fortunately, the 45B is tougher than a regular 45.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 15, 2019, 05:01:26 PM
Thanks PJ. I'm ok, I'm just kicking myself for making that mistake. I had lots of chances to catch it - first, when I ordered it, second when I received the resistors and checked their values, and third when I installed it.  But an "R" looks a lot like a "K" when you're looking for "8K2".

Any chance the amp can be run with the 2K cathode resistors, or am I courting more harm?
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on January 15, 2019, 06:39:55 PM
Any chance the amp can be run with the 2K cathode resistors, or am I courting more harm?
That's not going to cause any harm, you'll just be down on available power.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 16, 2019, 03:00:35 AM
Thanks PB.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Jamier on January 16, 2019, 10:20:23 AM
Derek,
          when you removed the 0.13 ohm heater resistors, what value did you replace them with? I don't have the DC filament kit so I have 0.15s in my amps, but perhaps you are referring to the second set of resistors that are added to the socket with the DC filament Kit.

Jamie
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 16, 2019, 12:22:55 PM
Hi Jamie - Yeah, the DCF calls for the addition of 0.13 ohm resistors in parallel with the 0.15's. So, as per PB's instructions, I simply removed the 0.13's and left the 0.15's in place and got lucky with the resulting DC heater voltage.  I think this is specific to SII's with the DCF.  PB's original instructions for stock SII's (or at least without the DCF upgrade) calls for swapping in 0.22 ohm 2+W resistors for the 0.15's. I would go with that. PB's instructions are quoted on page 1 of this thread.

cheers,

Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Jamier on January 16, 2019, 05:14:49 PM
Derek,
      Thanks for your reply. Don't beat yourself up over your mistake.Everbody in this hobby has made their share of those. I fried some $400 tweeters once upon a time.I'm going to make this conversion eventually, after I get a few work items off my plate. Thanks for being the trailblazer on this.

Jamie
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 17, 2019, 04:10:39 AM
@PB - I installed the 8K2s in parallel with the 2Ks.

VDC between pins 1 and 4 is now 2.76 (so out of spec; spec is 2.5 +5% tolerance).  What do you suggest I sub for 0.15R's?

Other voltages:

1-  365-366
2-  386
6-  60.6
7-  191.3
14- 192
15- 60.4
19- 386
20- 365.5
21- 61
22- 62.8
24- 59.8
25- 60.8
27- 398
30- 402-404
31- 404-405
34- 398
36- 61.1
37- 60
39- 63.3
40- 61

Many thanks,

Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on January 17, 2019, 04:35:30 AM
VDC between pins 1 and 4 is now 2.76 (so out of spec; spec is 2.5 +5% tolerance).  What do you suggest I sub for 0.15R's?

It shouldn't change based on the 8.2K resistor installation, but either way a 0.155R or a 0.16R resistor in place of each 0.15R resistor should get you back down to the proper range.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 17, 2019, 04:51:20 AM
Thanks PB.

While you were posting, I tried to calculate the value myself, but got the wrong answer. Can you point out where I went wrong?

My reasoning was as follows:

If 2.76V is dropped across a 0.3 ohm resistor (0.15 + 0.15), that means a current of 9.2 amps (that seems high to me).

If I want 2.5V, and R = V/I, then I get a combined R value of 0.27ohms - or 2 * 0.135 ohms.

Many thanks,

Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on January 17, 2019, 05:06:42 AM
Now that I think more about it, you did those filament measurements with the 8.2 ohm cathode resistors, so everything coming out of the power transformer would be very low. 


If 2.76V is dropped across a 0.3 ohm resistor (0.15 + 0.15)
The 45 filament is in there too.

You need to drop an extra 0.26V. 45 filament current is 1.5A.  0.26V/1.5A=0.173R.  This is the total addition you need, so just increase each resistor by about half that, or 0.08R. Something like this resistor would work ok:

https://www.mouser.com/ProductDetail/Vishay-Dale/CPF1R16000GNB14?qs=sGAEpiMZZMtlubZbdhIBIN9c7v76BNFlN04yaEgXCqY%3d (https://www.mouser.com/ProductDetail/Vishay-Dale/CPF1R16000GNB14?qs=sGAEpiMZZMtlubZbdhIBIN9c7v76BNFlN04yaEgXCqY%3d)

Do note that when you move this far down the trail, unlike the Stereomour I, you really don't want to plug 2A3s into an Steremour 2 that has been converted for 45 use, especially if you use the 1W dropping resistors to trim the filament voltage00. 
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 17, 2019, 05:19:06 AM
Thanks PB - yeah I not only forgot about the filament resistance, but failed to take into account that when measuring pin to pin, I'm not measuring the drop across the 0.15Rs b/c I'm measuring between them.

I have 0.33 and 0.3 ohm 3W resistors on hand that if combined in parallel will give me about 0.157 ohms. I am going to try that.

cheers and many thanks,

Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 17, 2019, 08:43:48 AM
My magic R-value for replacing the 0.15 ohm heater resistors turned out to be 0.25 ohms , for a combined value of 0.50 ohms.  With a 0.25 R swapped for each 0.15 R, I get 2.52V (avg) on one tube and 2.535V (avg) on the other.

[Edit - May 16 2019: Now that the amp has been burned in, I checked the heater voltages again and found that they had crept up a bit (about +0.02V). My new magic numbers are a combined 0.57 - 0.58 ohms per pair of resistors on each socket : 0.30 and 0.27 on one socket and 0.33 and 0.25 on the other. This gets me to a heater voltage averaging 2.5V +/- 0.005]

In case it is useful to someone, here are my DC voltages between pins 1 and 4 of the EML 45Bs for various R-values I substituted for the 0.15 ohm Rs:

0.157 ohm: (0.33 and 0.3 in parallel): 2.7V (avg)
0.18 ohm: 2.67V (avg)
0.20 ohm: 2.62V (avg)
0.22 ohm: 2.59V (avg)
0.25 ohm: 2.53 (avg)

The above data may suggest that the drop in voltage was not linear (e.g., going from 0.18 to 0.20 resulted in a 0.05V drop, while going from 0.20 to 0.22 resulted in only a 0.03V drop. This is because I tested the increasing R-values on alternating tubes - i.e., 0.18 on Tube 1, 0.20 on Tube 2, 0.22 on Tube 1, and so on.  The same 0.25 ohm value on both tubes resulted in a 0.015V difference between the filament voltages. Factoring in the 0.015V difference suggests a linear drop of approx. 0.02V per 0.01 ohm increase.

*** Note: the above values were reached after 5+ min and then became stable. I tested the VDC for the 0.25 ohms resistors by waiting 20 min just to be sure. For anyone looking to do the conversion, I would recommend waiting until the amp is well warmed up before settling on a final R-value. In my SII, 10 sec or so after power-on my reading with the 0.25 ohm resistors was only 2.4V

These measurements were taken on a fully upgraded SII after making the following mods: 3K resistors replaced with 8.2K resistors, removal of 0.13 ohm resistors that ran in parallel with the 0.15Rs, and swapping red and black wires from the plate chokes. I did not make any changes to the 130 ohm Rs.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on January 17, 2019, 09:33:16 AM
My magic R-value for replacing the 0.15 ohm heater resistors turned out to be 0.25 ohms.  With a 0.25 R swapped for each 0.15 R, I get 2.52V (avg) on one tube and 2.35V (avg) on the other.
Does this follow one particular tube if you swap it between channels?
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 17, 2019, 09:49:55 AM
Sorry PB. Typo! I meant 2.52V on one tube and 2.535V on the other, not 2.35.

I am treating the difference as trivial.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on January 17, 2019, 09:52:10 AM
Ah, yeah, that's better. 
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 18, 2019, 10:45:25 AM
Quick update: the SII-45B amp is up and running and sounds pretty good. I'm hoping that, at worst, I only took some lifespan off of the tubes with my resistor value fiasco. Still early days. I'll post some impressions after a month or so.

I have another SII kit in the early stages of assembly that I am building as a regular 45 to run with some used Raytheon 45's I have coming -- just to compare with the 45B amp. And then, depending on which of the 45/45B I prefer, convert one of the SII's to 2A3 to compare against my JJ 2A3-40s. Although I wonder if this is a good 2A3 comparator? I love their sound, but I've read that sound-wise they are closer to a JJ 300B than a 2A3.  If so, does that make a fully upgraded SII w/ JJ 2A3-40's a baby Kaiju?

cheers,

Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Joppa on January 18, 2019, 03:39:10 PM
It's hard to get a consensus on what is a real 2A3. By far the majority of 2A3s ever made are old-stock biplates (which look a lot like they are two 45s in parallel and in a single bottle). But the original version was a monoplate with the "harp" filament. It apparently had reliability problems; only a few were produced and they are now rare and expensive. The modern ones are mostly junior 300Bs, with a few like the JJ which is actually a 300B with a 2.5v filament. Can one actually talk about a 2A3 sound as distinct from a 45 or a 300B? I have my doubts.

A baby Kaiju based on the Stereomour kit would (IMHO) want 3K or 2.5K output transformers, and I'd add a larger plate choke as well. It would require 2A3-40s. or at least modern monoplates with the higher dissipation rating (usually 22 watts) - it would be too tempting to plug in regular 2A3s, which would overheat. That makes it less than practical for a kit. It might make 6 watts, which seems to me not enough more than the 3.5W of a 2A3 to be worth the effort.

My two cents.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on January 24, 2019, 02:33:47 PM
The newly built SII 45 hasn't even fully warmed up yet, and has zero burn in, and the Raytheon 45 tubes only test "good", but ... it sounds wonderful.  Wow. Liking this a lot. More detailed, but without being dry/analytical; instead more expansive/ethereal. Only early impressions; it'll be months before I get a good sense of the new amp.

Listening to Link Wray's self-titled album from 1971. It was recorded on a three-track in a converted chicken coop. It's kind of raw. I've listened to the album through the SII 2A3 (JJ's) and through 45B (EML), and it sounded great with both amps.  But it sounds absolutely stellar on the new SII 45. Sheesh, this is good.

... I might be a 45 convert.

Derek

Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Tom-s on March 09, 2019, 08:45:22 AM

... I might be a 45 convert.


And Derek, are you? :)

Love to hear your comparison of the 2A3 vs 45 Stereomour II with speakers and headphones.
With and without your balanced speaker outputs? Strong points/weaknesses etc.
Are they good/different enough to keep them both?

Keep us updated!
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on March 09, 2019, 10:46:23 AM
Hi Tom - I'm going to give it another month or two before posting more listening impressions.  I also want to give the EML 45Bs more time to burn in. I may not have damaged them with my resistor value fiasco. They are sounding pretty good as drop-ins for regular 45s and getting steadily better.

Am I a 45 convert? Yes ... but not completely. As of right now, I can't see converting the other SII amp to 45. My overall impressions haven't changed: the 45 really is magical/immersive and like being "inside" the music; whereas the 2A3 is more of wide-awake caffeinated experience where you as listener are very close to, but still separated from ("outside"), the music. While I mostly listen to the 45, I still sometimes prefer the 2A3.  And I no longer think I want monoblocks for listening through my LCD4s.  Putting the BeePre in front of the SIIs gave me a big boost in dynamics and perceived volume -- so no need to double up. 

cheers
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on April 14, 2019, 02:21:49 PM
Just a quick follow-up now that the SII 45 and EML 45B tubes have had more time to burn in.

I'd say I'm now a 90% 45-convert - meaning that 9 times out of 10 I'd prefer to listen to the SII 45 over the SII 2A3.

I still stand by my previous comments to the effect that, to my ears and in my setup, the SII 45 produces a magic and more enveloping sound whereas the 2A3 amp presents music in front of the listener as an object.  This is not a criticism of the 2A3 amp - just an observed  difference. 

The SII 45 produces a sound with more body and "mass". I don't know whether this is attributable to the 45 tube or to the fact that the 45 modification allows the OTs to go deeper in the bass, or some combination of both.

One place where the 2A3 amp continues to shine is on the attack of notes.  It punches quickly and decisively. In comparison, the 45 amp seems ever so slightly sluggish: as if the notes swell, taking slightly longer to reach full force. But I don't know which is more "faithful" to what was actually recorded. And let me be clear, the 45 amp has plenty of punch - it's not soft by any means. To use a boxing analogy: the 2A3 amp punches like Muhammed Ali - like a fast sharp knife. The 45 amp has a bit more Joe Foreman: slower but with a ton of follow-through.  On the flip-side, the 45 amp is so easy to listen to for extended periods; whereas the 2A3 amp by comparison can be a bit fatiguing.

Finally a big thumbs up for the EML 45B tubes. I am using them as a straight 45 drop in with no mods to the SII amp to take advantage of the tube's greater power handling capacity (I tried that initially and didn't notice much of a difference -- but I may play around with this again now that the tubes have burned in more). The tubes have taken a good while to come into their own (they are still improving every week). When brand new, I thought them clearly inferior to my various pairs of NOS and used OS 45 tubes from the 30's to 50's.  No longer. I now listen to the EML's almost exclusively.  And they barely get hot - I can hold my fingers on them with only minor discomfort (whereas the 2A3s and regular 45s get too hot to touch for more than a split second) - so I'm hoping the EML's will last a good long time.

cheers,

Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on May 22, 2019, 06:23:38 AM
@PB or @PJ: Question re parafeed cap value: In the initial post to this thread, the instruction is to increase the 3.3 uF cap to 5 uF, with 4.7 uF being fine. I went with 4.7 uF. But I just came across an earlier 2017 thread where PB suggested 8-10 uF.  What would be the mean of the target range: 5 or 8-10?  I'm guessing that the 8-10 uF applies if the plate choke is not rewired for 40H and instead left at 20H?  But I want to be sure.

My slow descent into audio nervosa has begun.  :)

MTIA,

Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on May 22, 2019, 06:26:09 AM
PJ's recommended cap value would be 5uF, with a pretty wide variation being OK.  I think in that post I used 3K for the transformer impedance accidentally instead of 4K.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on May 22, 2019, 06:27:41 AM
Many thanks PB ... my nervosa is subsiding.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on June 24, 2019, 03:07:00 AM
Just a quick note on parafeed cap value in case this is helpful to someone.


I originally installed a 4.7 uf 600VDC Clarity Cap, and subsequently added a 0.1 V-Cap CuTF in parallel for a total of 4.8uF.  PJ's recommended target is 5 uF.


I wasn't totally happy with the Clarity Caps -- I found them detailed but lifeless -- and so this past wknd I replaced the 4.7 UF caps with 2 X 2.2uF V-Cap ODAM caps, keeping the 0.1uF CuTF "bypass" cap, for a total of 4.5uF.  Result: a significant loss in bass weight -- the punch was still there, but the bass had less "mass" and "body". So I added another 0.22 uF CuTF cap in parallel, for a total of 4.7 uF and the bass returned. I was suprised that such a small difference (0.22 uF) could have such a big effect (I haven't done the math, so it is entirely possible that this is exactly what one would expect).


I am using my SII-45 with headphones that have a nearly flat frequency response to about 10 Hz. For those with speakers with a bass roll-off somewhere between 30 and 40 Hz, I suspect the effect of the parafeed cap value on the bass could be very pronounced. If I were using speakers with good bass range, I'd probably try to hit PJ's target 5.0uF and maybe even go a little higher -- e.g., 4.7uF and 0.47uF in parallel, for a total of approx. 5.2 uF. ... Just my thoughts and speculations ....


(Early impressions of the ODAM caps: detail is similar to the Clarity Cap CMR but with much more life and body).


cheers,


Derek



Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 24, 2019, 04:14:44 AM
When you do the 45 conversion, part of that involves connecting the entire winding of the plate choke between the 45 plate and B+, which is 40H instead of the 20H in the 2A3 configuration.  This is not possible with the 2A3 because it draws more current, but the reduced current drawn by the 45 allows this connection.  This change in conjunction with changing the parallel feed capacitor will work to improve the low end frequency response.  The power bandwidth of the OT-2 doesn't seem to be the limiting factor in this situation.  If you want to go for the high power 45B, then the plate current goes back up, and you need the other connection.

The Lundahl LL2743 may work, but it's a little off in terms of the options for the air gap. The Sowter 8985 would be the most appropriate aftermarket choice, but it's 50H/40mA, so you're not gaining much over what we provide. 

It kind of sounds like what you may want to do is build the Stereomour stock, then sort out the mods to get to #45s, then do a scratch build with all aftermarket parts.

Once I get the BeePre rebuilt, my plan is to rebuild the SII-45 (w/ EML 45B tubes) to see if I can get closer to the Kaiju's performance. So, I've ordered: (a) Lundahl 70H/160 DCR plate chokes rated for 60mA DC; and (b) Sowter "mumetal sandwich" 5K parafeed OPTs (getting custom 4Ks was too pricey and would also have necessitated a lot more parafeed capacitance when paired with the 70H chokes - also pricey when using V-caps).

Question: @PB or @PJ: can you tell me the DCR of the stock PC-3 configured for 40H, if known?

I ask b/c I'd like to estimate the effect on plate voltage of the new 160 DCR chokes. Eventually I will try B+ of 450V-500V, but that will require a new PT (I think I can squeeze at most another 20V out of the stock HV power supply by replacing the 130Rs with lower resistance chokes - but that only gets me to 400V and change). But I will stick with the stock PT for the initial test builds.

many thanks in advance, Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on October 24, 2019, 04:43:09 AM
You have the stock chokes in your amp, throw a meter across one! (it's more than 160R BTW)

If you're going to 5K, then moving to the book operating point that's 275V P-K and 36mA will work well. 
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 24, 2019, 04:51:49 AM
You have the stock chokes in your amp, throw a meter across one! (it's more than 160R BTW)

Hah! Yes, I was going to do that but got confused by something posted by Jac van de Walle about not using Digital ohmmeters on "tone transformers" b/c of core magnetization, but just reread it and now see that this is about running DC into OPT with no gap - so not a concern with a plate choke.

So I will measure. Good to hear that that stock is more than 160 DCR, though!

cheers and thanks, Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 25, 2019, 10:08:16 AM
Sowter is experiencing some delays and won't be able to make the 5K OPTs until late January, so I am taking a serious look at a pair of Lundahl "amorphous core" parafeed OPTs. Datasheets are not available for their parafeed models, but I gather that they are modified versions of their push-pull counterparts.  I'm considering their LL1679 model which allows for wiring for 9K7, 4K5 and 2K6 primaries which will give lots of room for experimeting with different setups. The P-P version, after factoring in the estimated 50% power reduction that comes from using the amorphous metal, should be capable of the following max power outputs @30Hz: 22W @ 9K7, 58W @ 4K5 and 94W @ 2K6. Since I'm interested in power to below 20Hz, my uninformed guess is that these max power figures may need to be further reduced by as much as 2/3s.  Assuming that the parafeed version (which weigh the same as the PP: 2.5 kg each) would have the same power handling specs, this is plenty more power handling capability than I "need" (but not more than I "want"  ;D)

@PJ or @PB: Before I commit to the Lundahls, is there anything I should be asking about them to ensure that they are in fact ideally suited to parafeed use? They are supposed to be specially made variants for parafeed, but I want to be as a certain as I can that they are suitable before committing b/c they would be an expensive mistake (and I've already made a few expensive mistakes this year).

many thanks, Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on October 25, 2019, 10:35:00 AM
January isn't that far away.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 25, 2019, 10:55:51 AM
January isn't that far away.

Yeah, but I'd really like to be able to play around with the rebuild earlier. And the ability to change primary impedances make the Lundahl a 3-in-1. Jac van de Walle reports that the "best" performance (output power, distortion, damping) from the 45B was achieved using this transformer wired for 9K7 (actually, his website states it was 9K2 but I think this is a misprint) - so I'd like to try it.

cheers, Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on October 25, 2019, 12:51:14 PM
You could perform the 4K vs. 8K experiment with our iron and draw your conclusions.  This doesn't require buying new transformers. 

I do not personally consider Lundahl iron to be an upgrade over what we provide.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 25, 2019, 03:44:03 PM
You could perform the 4K vs. 8K experiment with our iron and draw your conclusions.

The OT-2 can be wired for 8K?

Quote
I do not personally consider Lundahl iron to be an upgrade over what we provide.

Huh. I would have thought that at the very least a larger OPT, other things being equal, and up to a point, would have better bass response.  Is the Kaiju's better bass just a function of the 60H plate choke - and the larger OPT has no role?

many thanks, Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on October 25, 2019, 04:00:30 PM
The OT-2 can be wired for 8K?
Yes, in the SEX amp it is setup as an 8K transformer.  You just wire the transformer for 4 ohms when using an 8 ohm load.  The design splits the difference a bit in terms of 4K and 8K performance, though in practice this isn't particularly obvious.  I would mention, however, that if you tried to use it as a 12K or 2K transformer, I would expect some frequency response issues that were audible and easily measured.

Huh. I would have thought that at the very least a larger OPT, other things being equal, and up to a point, would have better bass response. 
I had a pair of 45 amps in my workshop earlier this year with Hammond 1628SE output transformers.  They are huge 30W series feed output transformers.  The bass was decent, but the high frequency response was a mess among other issues.

Is the Kaiju's better bass just a function of the 60H plate choke - and the larger OPT has no role?
They both work together.  The Kaiju uses 3K output transformers, so the demands placed upon the plate choke aren't as crazy as they would be with a 4K or 5K load.  Even with that relief, the Kaiju plate choke has more inductance anyway.  The Kaiju OT is larger, which also helps with low frequency response at higher power.  For a #45 that makes 2W at most, going larger than the  iron we provide is a difficult decision to rationalize. 

Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 25, 2019, 05:41:02 PM
Many thanks PB.

For a #45 that makes 2W at most, going larger than the  iron we provide is a difficult decision to rationalize.

Ah. I should have stated that I'll be going as high as 4.5W, maybe even 5W, since the SII-45 rebuild will be purpose built for the EML 45B (which is the only tube I use with the amp in any event).  The 45B has a max output of 5.2W, although Jac has hinted that this may be a conservative estimate.  I think the higher power output configuration should make a better comparator for the Kaiju's 8 wpc.  Some of the better bass I hear in the Kaiju may be power related. Dunno. But I'd like to find out.

Edit: And I should also clarify that the Lundahl OPTs I am considering are parafeed, not series or push-pull. They are zero gapped.

cheers, Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Joppa on October 25, 2019, 09:03:54 PM
There are a lot of things going on with this, too many to do more than mention in a single post. Here are (I think) the main ones:

* OPT inductance, which is much smaller at very low signal levels and usually sets a LF frequency response limit. Nickel cores have higher small-signal inductance.

* The frequency response at mid levels extends much lower than the power bandwidth.

* OPT saturation at high levels sets the power band lower limit. Nickel cores saturate at much smaller signal levels.

* Plate choke inductance

* Parafeed capacitor value, which if done right maintains a resistive load to a lower frequency than the choke alone, reducing tube distortion (but not transformer effects) at the lowest frequencies

The trick is to balance all these effects, which interact - they are not independent of each other. I've been working on this (in my own desultory fashion) for 20 years and I'm still learning.

The high frequency performance is a whole 'nother issue  :^)
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 26, 2019, 03:57:56 AM
Many thanks PJ. This is a very helpful summary.  In playing around on paper with different possible configurations, I have been guided by three things, mostly taken from guidance you have posted previously:

(1) Other things being equal (which they likely never are), more inductance in the plate choke and OPT = more better. 

 (2) The tradeoff (inverse relationship) between distortion and power from either (a) increasing OPT impedance, and/or (b) moving to mumetal (and presumably "amorphous") cores. As you stated:

Output transformer - keep the stock 4K, it is already overkill for a 45 in terms of bass handling capabillity. You might consider a Magnequest EXO-45/46 if you can get one with an all-nickel core, but it's a tradeoff - the 5K impedance reduces tube distortion and the nickel core reduces transformer distortion, but the physically smaller core and nickel laminations both reduce deep-bass power capability and the 5K impedance reduces available power full-range. (These effects would be very subtle.)

 Since I'll be using the EML 45B at >2W output (possibly as high as 5W), I figured a bigger OPT should be a good thing, provided it is a well made parafeed type -- particularly as I will be (a) using either a Sowter "mumetal sandwich" OPT or a Lundahl "amorphous core" OPT, and (b) if I get the Lundahl, experimenting with going as high as 9.7K primary impedance (with higher plate voltage and a difference PT to get me there).

(3) Your rule of thumb that the optimal parafeed cap value = 2*L/R*R (where L is plate choke inductance and R is OPT impedance), and that any value twice or half as big will work. I plan to use the midpoint - i.e., what your formula suggests.


There are a lot of things going on with this, too many to do more than mention in a single post. Here are (I think) the main ones:

* OPT inductance, which is much smaller at very low signal levels and usually sets a LF frequency response limit. Nickel cores have higher small-signal inductance.

[...]

* OPT saturation at high levels sets the power band lower limit. Nickel cores saturate at much smaller signal levels.

From what I've read, it sounds like mumetal and amorphous (glass metal) cores have similar effects as compared to silicon steel. So I have assumed that if one switches from M6 to one of these fancy core materials, inductance goes up but the core will saturate twice as easily (just a pure guess that I hope is good for estimating worst case scenarios). So in making the switch I need to double the size of the core to keep saturation levels the same. And if I want to decrease saturation levels, I need to go even bigger still.

Quote
* Plate choke inductance

I've ordered Lundahl plate chokes spec'ed as 70H @ 60 mA, with 160 DCR. 

Quote
* Parafeed capacitor value, which if done right maintains a resistive load to a lower frequency than the choke alone, reducing tube distortion (but not transformer effects) at the lowest frequencies

As stated above, I will be following your 2L/R*R formula.

Quote
The high frequency performance is a whole 'nother issue  :^)

The effect of different iron and different OPT impedances on treble will be interesting to hear. The Kaiju treble is superb and has really "opened my ears" to how wonderful a treble-centered (to my ears) presentation can be, whereas I usually gravitate to a more mid-to-low low centered presentation - which the SII and the EML 45Bs provide (but lacking the detail and punch of the Kaiju - again, to my ears).

Edit: And I almost forgot, I would very much appreciate any guidance you can provide about what if any questions I should ask about the Lundahl OPTs before committing. For example, I read an older post from you (PJ) on AA to the effect that PP OPTs are configured with a center-tap that is meant to be at AC ground potential, whereas parafeed requires the B+ connection to be at AC ground potential. So I assume that the parafeed version of the Lundahl OPT I am considering should have no center tap, and that maybe I should inquire about whether this is the case?

cheers and thanks, Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on October 26, 2019, 06:16:53 AM
If I am remembering correctly, you're using these with headphones right?
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 26, 2019, 07:14:59 AM
If I am remembering correctly, you're using these with headphones right?

Yeah, my Audeze LCD4 heaphones. With BeePre feeding Kaiju, I do most of my normal (but admittedly, loud-ish) listening with BeeQuiet set to -18db.  The extra power isn't overkill. When I only had the SII-2A3 I could run out of volume/headroom on some tracks - and this was when wired for 16 ohms.

I imagine the same setup would blow the drivers in most other headphones.

cheers, Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: 2wo on October 26, 2019, 07:21:42 AM
Regarding the center tap, Lundah uses a number of separate windings on both the primary and secondary that you connect in various series and parallel combinations to get the  impedance that you're looking for.  Theoretically you can add a tap  wherever two windings join, center or otherwise but there is no built in CT...John
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on October 26, 2019, 07:30:06 AM
The manufacturer indicates that about 10V from the amp will be adequate for the LCD-4.  You won't get this from a #45 amp or a #45B amp unless you get custom wound output transformers with higher impedance taps to make more power available.  You will get this from a BeePre, and probably even on the 8 ohm OT configuration because the load is light.  The huge downside to the custom transformer taps is that the noise floor will absolutely come up when you do this.  I just yesterday finished a #45 shunt regulated headphone amp with 125H Magnequest chokes and TL-404 5K autoformers that are tapped at a ton of different spots for lots of impedance choices.  While this amp is very quiet for a #45 amp, the noise floor comes up pretty quickly.

The Mainline on the high impedance setting should be quite satisfying with these headphones.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 26, 2019, 07:33:08 AM
there is no built in CT...John

Many thanks John. That clear that up. The funny thing is: I had looked over the datasheet for the PP version of the transformer a bunch of times and it clearly showed what you describe: no wires, just a large number of winding taps that you connect together, for different configurations - but despite the answer staring me in the face, I didn't put 2 and 2 together.  Amazing (to me, anyways, probably not to others) how often I do things like this.  ;D

Thanks for pointing this out.

cheers, Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 26, 2019, 09:23:34 AM
The manufacturer indicates that about 10V from the amp will be adequate for the LCD-4. 

Never thought to look at that since voltage requirements isn't a quoted spec for the headphones. But i think I see how you got there: P = I-sqr*R, so with Audeze's recommended 500 mW, I = 0.05 A, and so V = 0.05A*200R = 10V. 

I'll have to think about this more. I only recently clued into how output impedance and load interact: high load to output impedance ratio should maximize voltage dropped across the load; but setting R-load = output impedance maximizes power transfer (I haven't actually demonstrated the latter principle for myself - b/c I can't remember the calculus needed to do so, and so am simply taking this on faith until I find the time and gumption to relearn some math and probably newly learn a bunch more (complex numbers and phasors are somewhere in my future)). If my foregoing understanding is correct, then that means the SII-45B isn't capable of 10V and is instead geared for high current?  And my headphones are power-starved? Need to think/read about this more.

And I'm not sure what to make of the manufacturer's stated specs. They keep changing. When I decided to buy the LCD4s (used for the same price as a new pair of LCD3s), Inner Fidelity had done measurements and stated than the LCD4s needed about 500 mV (Volts not Watts) to reach 90dB. Around the same time, Audeze was recommending amps capable of "at least 4W" (without specifying more) for the LCD4s and stated that the phones could withstand up to 15W of momentary power (that stat has since disappeared - and they now claim that all of their over-ear phones are good for 5W rms).  And now (I just looked) Audeze states that all their over-ears, except the LCD4, which range from 15 ohms to 110 ohms input impedance, work best with ">250 mW". But they recommend >500mW for the LCD4s. 

I'm not sure how reliable or clear their specs are. When I first got the LCD4s, I picked up a SS headamp that on paper looked more than capable of driving them that cost about $425.   It was 4 wpc  with high, medium and low impedance, and capable of delivering 1500mW into 300Ω. Result: sounded like hell - lots of sharp treble, not enough volume and it sounded bogged down and muted if there was lots of bass. I was very disappointed. And that thing got good reviews (still does). One reviewer, the guy I bought my LCD4s from, even recommended the amp for LCD2, LCD3 and LCD4z (but not, conspicuously, the LCD4 - which is interesting, b/c he still owned my LCD4s at the time and was using them as his main "reference" set -- since replaced by the Abyss 1266).  Better sounding, amazingly, was the Massdrop "CTH" designed by Cavali -- it was too quiet, but it sounded good.  So I started fussing over finding amp for them (after the miserable failure of the SS amp that on paper looked ideally suited) I came across a bunch of comments on various forums suggesting that Audeze's LCD4 recommendations were way off and were incorrectly based on the specs for their other phones.  So I dunno. 

So the search was on for amp to pair them with. And that's what landed me on this forum 2 or so years ago. I had already built a Crack w/ SB for my Massdrop HD-6XX and really liked the sound, so I figured maybe a higher power BH amp would do the trick. And it did: the headphones sound amazing with BeePre and either SII or Kaiju.  Better than I've heard. I've not listened to many high end systems, but I have a friend with a top-of-the-line Linn system that costs a small fortune - it sounds great (a little too analytical and dry for my tastes, but with great detail, punch, etc.). I'd take my headphone system over his 2 channel system any day (except for resale value).

Quote
The Mainline on the high impedance setting should be quite satisfying with these headphones.

Well, one of those might be in my future.  But based on my past experience with that SS amp that could put way more than 500mW into the LCD4, I don't think picking an amp based on the manufacturer's specs is the way to go. I don't trust their specs - they've always been kinda unclear.

It would be great if someone posted the results of a listening test comparing the Mainline on hi-imp versus the SII with planars - say the LCD3s which are 110 ohms impedance (which looks to be the closest in the LCD series to the LCD4).  Maybe I will one day!  I would be absolutely shocked if the mainline could beat the combo of BeePre with Kaiju on the LCD4s - the sound is, as I stated above, literally the best I have ever heard. ... But maybe it does

cheers, Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on October 26, 2019, 12:11:46 PM
I'll have to think about this more. I only recently clued into how output impedance and load interact: high load to output impedance ratio should maximize voltage dropped across the load
The ratio establishes that the output of the amplifier won't vary too much as the load impedance changed (speakers rarely have a flat impedance curve).


but setting R-load = output impedance maximizes power transfer
IIRC, you get max power when the load impedance is about twice Rp. The loss of power for going to 3xRp is very much worth the trade-off of higher damping and lower distortion.


 If my foregoing understanding is correct, then that means the SII-45B isn't capable of 10V and is instead geared for high current?
Well, the output stage will swing about 100V RMS, so a 10:1 step-down will get you to about 10V.  It is, however, my suggestion that you wouldn't want to do this, especially if you have to spend a crap ton of money to perform the experiment. 

  And my headphones are power-starved? Need to think/read about this more.
If a Kaiju, especially wired for 16 ohms, is giving you a huge performance increase, it wouldn't be unreasonable to infer that this is a possibility.



 Inner Fidelity had done measurements and stated than the LCD4s needed about 500 mV (Volts not Watts) to reach 90dB.
That's a typo.

 Around the same time, Audeze was recommending amps capable of "at least 4W" (without specifying more) for the LCD4s and stated that the phones could withstand up to 15W of momentary power (that stat has since disappeared - and they now claim that all of their over-ear phones are good for 5W rms). 
They are trying to write specs that can match up with products.  A solid state amp that will put out 4W into an 8 ohm load will be a pure voltage source capable of 5.6W, which is 160mW.  A tube OTL amplifier that can put out 4W into 8 ohms will put out far more into 200 ohms.  In fact, a Crack could be modified to deliver this kind of power.




Well, one of those might be in my future.  But based on my past experience with that SS amp that could put way more than 500mW into the LCD4, I don't think picking an amp based on the manufacturer's specs is the way to go. I don't trust their specs - they've always been kinda unclear.
Well, we have decades of power amplifier development to make amps that work well into low impedance loads from say 1 ohm to 16 ohms.  Headphones are all over the place, and it's challenging to make an amp that will drive 16 ohm headphones really well and 600 ohm headphones really well, though with an output transformer it's not as tough. 
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 26, 2019, 01:49:07 PM
Many thanks PB.

The ratio establishes that the output of the amplifier won't vary too much as the load impedance changed (speakers rarely have a flat impedance curve).

This I get (I *think*) - I understand (perhaps simplistically or even erroneously) the good regulation as a consequence of the voltage divider relationship where source resistance/impedance is the first resistor (R1) in series with the voltage source and the load is the second resistor. If R2 is much greater than R1, then small variations in R2 won't cause wild fluctuations in regulation; whereas if R2 is close to R1, the same magnitude of fluctuation will cause a big decrease/increase in voaltge dropping across the load. 

Quote
IIRC, you get max power when the load impedance is about twice Rp. The loss of power for going to 3xRp is very much worth the trade-off of higher damping and lower distortion.

I really have no clue here. I was just paraphrasing what I remembered reading in Horowitz and Hill, The Art of Electronics 3rd. ed.(my late night bedtime reading, along with Ott's latest edition on dealing with noise and interference - thanks Jamie!  :) ) I just looked it up again - from the end of p. 11: "Show that R-load = R-source maximizes the power in the load for a given source resistance. Note: skip this exercise if you don;t know calculus, and take it on faith that the answer is true." I can;t remember (assuming I ever knew) the calculus necessary to prove this, so I did as instructed and "took it on faith."

Quote
  If a Kaiju, especially wired for 16 ohms, is giving you a huge performance increase, it wouldn't be unreasonable to infer that this is a possibility.

The Kaiju just sounds better than the SII-45 (which sounds better than the SII-2A3). The K is cleaner and punchier and the treble is amazing. In comparison, the SII-45 sounds a little hazier and less decisive. Is it a huge step up in performance? Dunno. The difference is small, but appreciable. Kind of like a smeared mirror or window: that last fraction of a percent of dirt makes a huge difference; but quantitatively, as a percentage of the
amount of beginning dirt, it is insignificant.  At the same time, I imagine there would be no appreciable difference were I using a really cheap DAC, preamp and headphone set - they would add so much "dirt" that the improvement would be buried by the noise floor.

Quote
That's a typo.

Well I obviously have no basis to assert things are one way or the other and am just relaying what I read. So I looked it up again. IF repeats the less than 0.5V figure twice in the their measurements.  Here's the first instance:

"Volts RMS required to reach 90dB SPL: 0.482 Vrms
Impedance @ 1kHz: 206 Ohms
Power Needed for 90d BSPL 1.13 mW
Broadband Isolation in dB (100Hz to 10kHz): -2 dBr"

Second instance (same measurement page):

"The LCD-4 needs 482mVrms to reach 90dBspl at the ear. These headphones will run quite a bit more towards the top of your volume dial than most. But their 200 Ohm impedance means that they're only moderately less efficient than most."

(see http://www.innerfidelity.com/content/technologically-impressive-lcd-4-planar-magnetic-headphone-measurements#S6BkJ5yiLskokcbb.99)

 
Quote
... a Crack could be modified to deliver this kind of power.

That's sounds like a fun experiment. Could you elaborate on the required mods? I have a mostly intact Crack collecting dust that I will happily experiment with. 

But in the end: while I can't discount the possibility that I am missing out on what my LCD4s are capable of (and this is a concession I make based purely on logic applied to my acknowledged lack of both empirical experience and knowledge about the science of all this - but my ears say "no way"), I find this almost impossible to even imagine. The sound coming out of them when fed by the BP and K (or by the SII's, to a slightly lesser extent) is superb. Is better sound possible? Probably - I bet the K could be built with even better OPTs that cost thousands or even tens of thousands of dollars more that would make it sound better. Would the Mainline sound better than the BP and K? Maybe one day I'll get to find out. ... But I doubt it.  And if so, I'll have the makings for a helluva 2 channel system - I'll just need to buy Jagers, plus move to a place in the country where I won't have the cops at my door every night  ;D)

cheers, Derek



Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on October 26, 2019, 02:15:48 PM
I suppose the 0.5V for 90dB will also depend on how far the microphone is from the driver, so perhaps there just isn't anything to be learned or gleaned from that measurement.

For the Crack, we would move from analysis in volts to analysis in mA.  We'll assume that you want 500mW into 200 ohms, which requires 70mA peak current swing.   If we assume about 100V at the cathode of the 6080, then that's 7W of dissipation through the Speedball if we set it to 70mA.  Case to junction thermal coefficient of the TIP50 is 3.125C/W, and the heatsink is 7.5C/W.  With 7W dissipated, that will be 75C rise, so you'll see a constant 100C during operation.  This is the absolute maximum dissipation that you could really run on these for very long, and putting the Crack over a laptop cooler to circulate air with fans will be a very good idea.

To set the large Speedball board for 70mA, R1 would need to be about 12.2 ohms 1/4W.  R2 would need to carry 7mA, so 25K/3W.

The 270 ohm resistors in the power supply will blow with 160mA flowing through them.  They would also drop a ridiculous amount of voltage.  I would use a pair of Triad C-14X chokes instead, which are rated for the current and have about half the DCR of the resistors, so the extra voltage drop won't be such a problem.  The power transformer will get hotter, though I suspect not harmfully so. 

The last thing I had to look at was to make sure the bias voltage of the 6080 doesn't get too low, as grid current can become a problem.  We are looking at 70mA of plate current and a plate voltage that will be around 80V, and there's still ample bias voltage available for that.  While staring at the curves, it also doesn't hurt to draw a 200 ohm load line to look at what kind of swing you get.  The problem you can run into here would be running into the 0V grid voltage line well before hitting 0mA on the other side.  With the proposed operating point, you'll hit 0mA of current with the grid driven about +35V, and on the other side you'll get to 140mA with a bit less signal.  It will work, but have some nice warm fuzz for you with asymmetrical clipping when pushed hard.

Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 27, 2019, 06:49:38 AM
The manufacturer indicates that about 10V from the amp will be adequate for the LCD-4.  You won't get this from a #45 amp or a #45B amp unless you get custom wound output transformers with higher impedance taps to make more power available. 

I did some more reading this morning that i think clears this up. IN a FAQ, Audeze explains that the higher Watts recommendation is for transients. That makes sense to me since, according to a couple of online calculators I checked, the 97 dB/mV sensitivity of the LCD4 only requires 63 mW to get to 115 dB - which is pretty loud. 

Lundahl makes a headphone output transformer tapped for 4.6K/32, 5.4K/150 and 5.4K/600 ohms: LL2765. Assuming I can get it made for parafeed, do you foresee any problems with trying it?  Datasheet attached. 

I'd be curious to hear how the SII-45 performs driving the LCD4 with a ton more headroom.  The impedance/frequency plot of phones is nearly ruler flat, so I'm thinking the loss of damping with the secondaries wired for 150 ohms might not be a big deal.  But I suspect I'd need to pad down the signal, but not sure where in the BeePre -> SII-45 chain.

If it is workable, I could convert the SII-2A3 to run regular 45s with the LL2765, and compare it to the SII-45 rebuild for EML 45B.  I think that would be cool.

cheers and many thanks, Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 27, 2019, 06:53:29 AM
With 7W dissipated, that will be 75C rise, so you'll see a constant 100C during operation.  This is the absolute maximum dissipation that you could really run on these for very long, and putting the Crack over a laptop cooler to circulate air with fans will be a very good idea.

Hmmmm. Thanks for this PB. But I'm not sure I want to venture into the territory of potentially destructive testing! I'm not using the Crack but I'd like it to survive that so my son can use it down the line.

cheers, Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on October 27, 2019, 08:54:35 AM
I did some more reading this morning that i think clears this up. IN a FAQ, Audeze explains that the higher Watts recommendation is for transients. That makes sense to me since, according to a couple of online calculators I checked, the 97 dB/mV sensitivity of the LCD4 only requires 63 mW to get to 115 dB - which is pretty loud. 
You can play a 60Hz tone into your headphones that sounds "loud" and measure it with your AC volt meter and make this determination yourself.

Lundahl makes a headphone output transformer tapped for 4.6K/32, 5.4K/150 and 5.4K/600 ohms: LL2765. Assuming I can get it made for parafeed, do you foresee any problems with trying it?  Datasheet attached. 
Yes, noise.  The 32 ohm output might be quiet enough.  I'd also want to see frequency response measurements for each of those secondary configurations.

The impedance/frequency plot of phones is nearly ruler flat, so I'm thinking the loss of damping with the secondaries wired for 150 ohms might not be a big deal. 
Damping won't be a big deal, but noise will be.

I'm getting the impression that you should just use the Kaiju.  It has the power you need and doesn't require a tube that one random company makes. 
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 27, 2019, 09:49:51 AM
Many thanks PB.
You can play a 60Hz tone into your headphones that sounds "loud" and measure it with your AC volt meter and make this determination yourself.

Yes, true. But I don't have a problem get loud enough. I'm just curious about whether more power for split-second transients is noticeable.

Quote
Yes, noise.  The 32 ohm output might be quiet enough.  I'd also want to see frequency response measurements for each of those secondary configurations.

Thanks, that's helpful. Does one component in particular contribute to the noise - e.g., is this heater/filament noise?

Quote
I'm getting the impression that you should just use the Kaiju.  It has the power you need and doesn't require a tube that one random company makes.

The Kaiju's definitely not going anywhere. And just be clear: I don't think there is anything wrong with my SII-45. This is project is mostly just for the fun/learning to be had: I want to see whether the SII-45 can be brought closer in performance to the Kaiju with my favorite 45 tubes, the EMLs (whether they are technically "45" tubes does'nt much concner me - they are drop ins for a regular 45 and to my ears sound better).

cheers and thanks, Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on October 27, 2019, 10:25:44 AM
Yes, true. But I don't have a problem get loud enough. I'm just curious about whether more power for split-second transients is noticeable.
If "loud" is 0.5V vs. 5V, doesn't that provide a ton of information for you about how critical more transient power would be?

Thanks, that's helpful. Does one component in particular contribute to the noise - e.g., is this heater/filament noise?
The #45.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 27, 2019, 11:44:29 AM
If "loud" is 0.5V vs. 5V, doesn't that provide a ton of information for you about how critical more transient power would be?

I'm just interested in testing Audeze's argument for having tons of power on tap: the brain interprets millisecond loud transients (e.g., 30-50 dB louder) that form the leading edge of notes/sounds as part of what makes things sound "realistic". Their argument can be found here: http://www.audeze.com/blogs/technology-and-innovation/sensitivity-impedance-and-amplifier-power (http://www.audeze.com/blogs/technology-and-innovation/sensitivity-impedance-and-amplifier-power) I understand them to be suggesting that the transient edge, because of its super short duration, doesn't register as "loud" in the brain, but as part of what the brain expects as part of the sound of something real (drum hit, hand clap, etc.). I'm not saying Audeze is right - but that seems to be why they say tons of excess power is necessary.

Quote
The #45.

Ah. Thanks. So the noise in inherent to the tube structure/performance itself.

cheers, Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Joppa on October 27, 2019, 03:03:30 PM
I'm just interested in testing Audeze's argument for having tons of power on tap: the brain interprets millisecond loud transients (e.g., 30-50 dB louder) that form the leading edge of notes/sounds as part of what makes things sound "realistic". ...


Lots of people say this. Recordings, however, virtually never capture more than 14-20dB of the transient peak. So OK, if you have your own microphones in Symphony Hall, and run your own wire from there to your living room, then this might be relevant.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 27, 2019, 03:45:14 PM
Lots of people say this. Recordings, however, virtually never capture more than 14-20dB of the transient peak. So OK, if you have your own microphones in Symphony Hall, and run your own wire from there to your living room, then this might be relevant.

Thanks PJ - On reflection, that makes immediate sense. I imagine that even with the microphones, capturing the full peak of the transients might be a challenge. I don't know anything about recording technology, but assuming mics make use of some sort of logarithmic translator of sound pressure to voltage signal, the receiving membrane would have to be insanely engineered to be able to deal with both low level and ultra-high level sound.

cheers and thanks, Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Joppa on October 27, 2019, 07:17:46 PM
I looked up my notes - the OT-2 (Stereomour/SEX output transformer) operating as an 8K transformer (SEX) saturates about 2.4 watts at 25Hz, which is 4.8 watts at 35Hz or 9.6 watts at 50Hz. At 4K ohms (Stereomour), it's 2.4 watts at 18Hz, 4.8 watts at 25Hz, 9.6 watts at 35Hz, and 19.2 watts at 50Hz. Measured inductance was 45H at 350 Gauss, gradually rising to 265H at 7000 Gauss (as high as I could go at the time).

For comparison, OT-5 in Kaiju at 3K ohms is good for 8 watts at 22Hz.

These calculations are for 29-gauge M6 grain-oriented silicon steel at 13,500 Gauss flux density - moderately conservative since power transformers will sometimes push the M6 flux density to 16,000 Gauss.

A quick look at that Lundahl shows the primary is always the same, at all nominal impedances - only the secondary taps change. That's exactly the same as OT-2. Looks like it will handle about 10 times as much power as OT2 at any of the above impedance/frequency combinations. I see a rated 150 henries for the small gap (parafeed), but at an unspecified flux density. It's common to measure this at a high flux, but I don't know how Lundahl does it.

I estimate from the specs that Lundahl does their power rating at 16,000 Gauss, which is about 40% more power than 13,500 Gauss, but - again - I don't have specs on their core material, and I'm making some guesses.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 28, 2019, 02:42:18 AM
Many thanks PJ.

I see a rated 150 henries for the small gap (parafeed), but at an unspecified flux density. It's common to measure this at a high flux, but I don't know how Lundahl does it.

I estimate from the specs that Lundahl does their power rating at 16,000 Gauss, which is about 40% more power than 13,500 Gauss, but - again - I don't have specs on their core material, and I'm making some guesses.

I have emailed Lundahl and inquired about this. From what I read, going to amorphous core roughly doubles the inductance but also greatly increases the saturation and so reduces power handling - but with all that extra power handling available, I think this should be OK. Hopefully Lundahl will respond with answers.

cheers and thanks, Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 28, 2019, 08:08:26 AM
I've heard back from Per Lundahl. No specs for Gauss, and nothing specific for parafeed or amorphous core, but maybe this can be calculated/estimated from the info he provides? He states:

"The primary inductance for LL1679/PP(silicon iron core) is 150H  with 25u airgap, so the inductance for the AM core in PPZ (0u airgap)  should be at least 150H or higher. Measured at no DC component, 50Hz, approx. 100V RMS signal swing."
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on October 28, 2019, 08:15:58 AM
So... Sowter 8983?
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 28, 2019, 08:27:58 AM
And in case it is relevant, here's what Lundahl says (online) about the difference between silicon steel and amorphous core versions of its transformers:

"The obvious measurable difference between our silicon-iron cores and amorphous cores is that the saturation flux for the amorphous core is approximately 33% less than for the silicon-iron counterpart. This is caused partly by a lower saturating flux level, partly by a smaller fill-factor due to the thickness of the amorphous sheets. As a result, power bandwidth is reduced by about 50%. (This means that if the max output power for a standard LL1620/40mA is 25W at 30 Hz, corresponding max. power for LL1620AM/40mA is 13W.)"
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 28, 2019, 08:32:36 AM
So... Sowter 8983?

I am clueless here. You guys left me in the dust as soon as the discussion went beyond my understandings that (a) other things being equal, bigger = more power, less saturation, and (b) amorphous may sound nice, like mumetal

I'm hoping PJ will jump in with more of his insight.

cheers and thanks, Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Joppa on October 30, 2019, 06:45:12 AM
Yeah, that was a blast of information without enough context. Apologies.

I was basically trying to assess the operation of OT-2 at 8k ohms impedance and high power. Bottom line - to compare with Lundahl, one should use the same saturation flux density and frequency. Lundahl uses 30Hz, and I estimate from their specs that they use 16kGauss. Under those conditions, OT-2 can handle 4.85 watts.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on October 30, 2019, 01:34:08 PM
Yeah, that was a blast of information without enough context. Apologies.

No apologies necessary! After your post I did a little reading and thought I'd take a stab at estimating "Bmax" only to find that you need to know the # of turns and cross-sectional area of the core - neither of which I know, and can't see a way to estimate them based on what I do. So how you are able to make estimations is a total mystery to me! And no need to try to explain - even were I to apply myself rigorously to learning this stuff, I am likely a very long way from being able to understand (but making slow and steady "progress": I am getting more accurate in identifying what I don't understand)  ;D

cheers and thanks, Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Tom-s on December 01, 2019, 02:41:23 AM
There is no optimum capacitance. Bigger is better, limited only by practical considerations such as the start-up voltage sequencing, physical size of the cap, or high-frequency cap problems (generally worse the larger the cap). There is a minimum size, set mostly by the low frequency limit and the margin you choose. The analysis for a minimum size is pretty complicated because it involves the output circuit (plate choke, parafeed cap, OPT, and power supply) as well as the load (speaker impedance function). In practice, 47uF is good. I've seen lower values down to 20uF but I would not try it myself unless I could audition alternatives in the target system.

I've searched the forum and this thread in particular to find out how the cathode bypass cap of the 45 would need to change.
This is because i'm planning on using a 30uf or 60uf oil bypass in the 2A3 SII and might want to change to 45's later on.
How would going from 2A3 to 45 change this equation? How do i calculate this myself?
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Joppa on December 01, 2019, 04:46:36 AM
I've never done the full analysis, or set criteria which might be used with such an analysis to select a "minimum" cathode bypass capacitance. As in other cases, there is no optimum; larger is better but with diminishing returns - where do you draw the line?

That said, the 45 conversion goes lower in frequency than stock, so I would not go below the 47uF previously mentioned. Use the 60uF in preference to the 30uF.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Doc B. on December 01, 2019, 06:45:38 AM
PJ's experience makes him pretty damned good at predictions. But at some point you have just dive in there, try some different cap values using his predictions as a starting point, take measurements and listen.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on December 01, 2019, 07:21:44 AM
I'll present my two lazy methods of looking at this...

#1.  Find a capacitor with a reactance that is 1/100th the value of the cathode resistor at 20Hz.  For a 1.6K cathode resistor, that's 50uF.  I don't have any analysis to back this up, but it's quick and dirty.   

#2.  Use this (http://www.mh-audio.nl/Calculators/CCBC.html) calculator.  Since we are interested in low frequency response, we can figure out the numbers for Rload and Rp based on the circuit itself.  A 40H choke (SMR wired for #45) has a reactance of about 5K at 20Hz, and the reflected load of the parallel feed output transformer is close to 4K.  The 5uF parallel feed capacitor will have an impedance of 1.6K at 20Hz, and this will be in series with the OT, so the Rload is 5600 ohms and the Rp is 5000 ohms.   I use 20Hz for the -0.1db box. For most of the other calculators on this website, there are formulas explaining how they created their calculators, but they are notably absent from this page.  When I put all these numbers in, that calculator spit out 44uF. 

I would imagine the Radiotron handbook has the appropriate formula in it, and that formula could be programmed into Excel to spit out cap values.  A part of me hopes that's what's going on with the MH-Audio calculator!
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Raymond P. on December 07, 2019, 01:37:11 PM
I am in the process of converting an SII to 45's and have some questions. But first, thanks to everyone here for the invaluable information to help me get started.

Ok, here's my situation. I'm trying to fine tune the filament resistor values, I have the DCF supply installed, and I have standard 45 tubes. Base on data in this thread, I started with a pair of 0.25 ohm resistors, then took measurements: DCF supply voltage = 3.4Vdc,  voltage across each 0.25 ohm resistor = 0.375V,  voltage across filament = 2.66V,  current through filament = 1.5A. This data was recorded after voltages stabilized.

So the filament current is at spec, but the voltage is 6.4% too high. To reduce the filament voltage, I can play around with increasing the resistor values, but if I did that, the current would go down (right?). So is there an achievable solution where the current is 1.5A and the filament voltage is 2.5V? Is hitting one target more important than the other? Any suggestions on what resistor value(s) to try next based on this data point?

Just to see if the filament is "behaving", I gave it 2.5Vdc with a power supply and it consumed 1.5A, so it seems ok.


Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Birkeland on December 07, 2019, 02:00:50 PM
The filament is not purely resistive, so reducing the voltage won't necessarily reduce the current. 

You need to drop an extra 0.16V at 1.5A, which calls for 0.11 ohms of extra resistance, which would mean 0.3 ohm resistors.


If you want a different way to achieve the same goal, you could draw another 0.3A through the filament supply, which you could do with an 8.2 ohm resistor across the filament (pins 1 and 4 on the socket).  It would need to be a 3W resistor.  This is totally OK since everything is rated for 2A3 use.


You don't have to be dead nuts on; the pickiest tube manufacturers would want 2.4-2.6V.

-PB
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Raymond P. on December 07, 2019, 06:43:33 PM
The filament is not purely resistive, so reducing the voltage won't necessarily reduce the current. 
That's interesting. Thanks, PB. I'll try 0.3 ohms next.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on December 08, 2019, 04:19:18 AM
The filament is not purely resistive, so reducing the voltage won't necessarily reduce the current. 

@PB - can you say a bit more about this? Since Raymond has the DC filament supply, that knocks out anything frequency dependent - so no impedance, right? So what would allow the filament to present a variable effective resistance?

cheers and thanks, Derek
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Paul Joppa on December 08, 2019, 04:54:05 AM
Resistance is a strong function of temperature. When the temperature goes up, so does the resistance - so the current does not increase nearly as rapidly as the voltage alone would suggest.
Title: Re: Stereomour II 45 Conversion - Anyone Do It Yet?
Post by: Deke609 on December 08, 2019, 06:10:47 AM
Many thanks PJ. That makes sense. Guessing that explains why superconductors are super-cooled.