Stereomour II 45 Conversion - Anyone Do It Yet?

[Paul Birkeland]

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. 

[2wo]

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

[Deke609]

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

[Paul Birkeland]

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...

[Deke609]

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.

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  ). 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.

[Paul Birkeland]

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. 

[Deke609]

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?

[Paul Birkeland]

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.

[Deke609]

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

[Deke609]

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

[Paul Birkeland]

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.

[Deke609]

Thanks PB.

[maryc27182]

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.

[Deke609]

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

[maryc27182]

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