Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Topic started by: Jim R. on January 21, 2011, 07:56:25 AM
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Would I have to first find a pair of Paramour IIs? Or, would it be possible to get the iron a la carte, the schematics, and any other special parts? I am fully capable of making my own chassis and top plates.
I've been trying some 45s in my Fi 2a3 monos and am somewhat smitten, but really want an amp optimized for the 45, and lots and lots of folks say the SR45s are fantastic amps.
Thank,
Jim
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We don't have power transformers for the Paramour anymore, so it might be easiest to find some used ones.
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I should have my stock output transformers for my Paramour I around somewhere. I never used them and went straight to the upgraded iron. If I recall, the chokes used in the original iron were repurposed for the upgrade. Let me know and I will dig around for them.
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Thanks, David, but after posting this I took a look on agon and saw a freshly listed pair of IIs and jumped on them. They are all paid for and will be on the way to me soon.
Dan, so what's next? :-)
Actually, I'm going to listen to these as they are for a while until the stereomour is finished (on the cornwalls) and then swap the stereomour in this system and start the conversion.
I'm psyched that I have a set of Paramours coming!
-- Jim
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The SR-45 is a fantastic amp. I built al la Stereomour with a common PS. You are going to want the iron upgrade for sure...John
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For some time I have been looking at a new version SR45. There are a few things I would like to change in the design, based on our experience with the original. Stay in touch; when you are ready to make the conversion I may have some refinements to the operating points, and I hope a new PC board with a heftier heat sink.
The original used the Paramour upgrade iron from Magnequest, with a 3K primary impedance. The Stereomour uses a 4K impedance, which is a bit better suited to the 45, but is not Magnequest quality. I don't know whether your Paramour IIs have the upgraded iron or not, but in either case it will be an interesting comparison with the Stereomour!
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Paul,
As far as I know these are stock, and I'm not even sure the seller built them as he doesn't have the manual. So, among other things I'll need to get a manual and whatever instructions there were for the SR45 conversion.
Any other transformers that will work -- exo 45, etc.?
I will stay tuned to whatever you have brewing, but for now, as I said, I really just want to get the flavor of the amps as they are, and then maybe do the basic 45 conversion next, and then maybe doc's grid choke mod.
John, thanks for the note, and actually a lot of this was due to the comments you've made here and elsewhere about your SR 45s.
All this and my cornwall rebuild should keep me busy and happy with projects for a while to come.
Guess I'm finally going to have to put the Carina on the block though -- great amp, just not a triode or DHT and I'm spoiled now, especially since I have speakers that can really bring the best out of them.
-- Jim
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For some time I have been looking at a new version SR45. There are a few things I would like to change in the design, based on our experience with the original.
Hi Paul,
Would you mind divulging the changes you have in mind? I'm getting around to putting a SR45-inspired amp together as well.
I say SR45-inspired because while I have the SR45 kit I don't have the Paramour II's. For iron, I'm using MQ nickel TFA-2004 Jr. outputs and BCP-15 (40mA/ 50H) plate chokes. I'll be following the schematic included with the kit, with the following exceptions:
* I got Heyboer to make me some power transformers. The PS will be 6AU4GT full-wave -> LC w/ MQ VanOfMonks choke and Panasonic caps.
* I'm planning on increasing the current by about 4mA through the SR.
* Swapping out the grid-leak resistor on the input 6CM7 for a Altec 42292A (2k:10k) step-up transformer + 10k pot.
Thanks. We can take this offline if you'd prefer.
John
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Hey Jim,
You might want to check out this writeup I did a while back:
http://www.bottlehead.com/smf/index.php/topic,361.0.html
It's been a couple of years since I did the conversion, but if
you have any questions just ask. I'll try to help if I can!
Mike
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Hi Paul,
I too would be very interested in any updates. My SR-45 was planed as a 2A3 amp using the BH upgrade Iron, I would not mind changeing it back and rebuilding the 45. Like I need an excuse to build something...John
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OK guys, I printed out my notes and will review them for the differences - hopefully, on the ferry tomorrow. Quick look, the main differences are a bigger heat sink for the C4S that feeds the shunt reg, and DC filament power for the 45.
At the time of the original circuit, I came up with a variety of operating points for various output transformers in the range of 3K to 5K impedance; no reason I shouldn't gather those into a table and post it.
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DC filament for the 45? You definitely just got my attention. Is that with the stereomour tranny or the PT2?
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No, none of the various Paramour/Stereomour/etc. transformers are suitable. I'll keep the details under my hat until I know whether this will work in the real world!
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Hi Mike,
Thanks for the link. I did read that yesterday after I knew that I bought the amps -- along with anything else I could find on the SR45. I appreciate the offer to help, and I may well be taking you up on that, once I figure out what I need to get in terms of parts and instructions on how to make the conversion.
Thanks much,
Jim
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OK, I went over my notes, and here are some comments:
* The original bag'o'parts (not a kit, no manual, "for experienced eXperimenters only") version was based on the upgraded Paramour II; specifically designed to use the Magnequest BH-5 transformer (3K impedance) and BH-6 plate choke. This is the amp Doc B uses on his Raal tweeters. It was designed to the constraints of the available power supply. The four limitations it had were 1) low shunt reg current, requiring the BH-6 to provide enough inductance for that to work; 2) AC filament power, 3) marginal heatsink on the C4S feeding the shunt regulator - it is not tolerant of high power line voltages, and 4) relatively low gain.
* I don't plan to do anything about the gain (item 4) above) - suck it up and use a preamp, guys! :^)
* At various times I suggested three different operating points for the 45, depending on the output transformer impedance:
3K impedance: 250v at 36mA (standard), 1300 ohm cathode resistor
4K impedance: 250v at 31mA, 1550 ohm cathode resistor
5K impedance: 250v at 28mA, 1830 ohm cathode resistor
These had inconsistent estimates of the available power which I won't repeat, but they were generally in the range of 1.5 to 2 watts maximum.
The lower 45 current allows greater shunt reg current, but that happens at higher impedances where more demands are placed on the plate choke inductance, so I don't think varying the load impedance this way affects limitation 1) above to any useful degree.
* The new design I am working on uses a different power transformer with greater current capability, which does address the shunt reg current question, item 1) above. It also (I hope) will allow a DC heater supply, item 2) above. I am going to use a much larger heat sink and a new PC board, which addresses item 3) - my target is to provide for reliable operation between 110v and 130v from the power line. The filament power is not regulated, however.
* The new transformer also provides a bit more high voltage, allowing the 45 to operate at 265v instead of 250v, plate to cathode. I'll run it at 35mA into a 4K impedance transformer.
* The original used a 6CM7 shunt reg/driver tube. This is sort of a 9-pin version of the 6DN7, and the Paramour II power transformer is (just) able to heat a 6DN7 as well. The 6CS7 looks better than the 6CM7 on paper, but with a hair less gain. Until I get to hear them all in this application, I won't have any guidance on which is preferred.
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Paul,
Thanks for all this.
Let's suppose I just want to work with what I have/am getting (and at this point I don't know if the iron has been upgraded or not as the seller wasn't sure), what would you recommend as potential suitable transformers? Stereomour? EXO 45 or 50? RH PF, or if I wanted to go custom, what would the specs be for inductance and RDC? Also, what about the plate choke? I have no idea what the specs on the original Paramour iron upgrade pieces are.
Also, as my speakers are 95/96 dB, I'd probably be fine with AC heaters, and if at a later date I wanted to change that, I can always build an external filament supply either based on the FC1, or maybe the diyhifi filament supply modules.
Funny, I've also been considering an extended FP III, so this may be coming sooner than I had originally planned.
I had also wondered about the 6dn7 as a possible driver/shunt reg tube, so glad to see you mention that.
Thanks again,
Jim
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... what would you recommend as potential suitable transformers? Stereomour? EXO 45 or 50? RH PF, or if I wanted to go custom, what would the specs be for inductance and RDC? Also, what about the plate choke? ...
Instead of a recommendation, I'll offer some assessment - theoretical of course since I haven't compared these myself in an SR45 circuit:
The best sounding transformer would be a TFA-2004 Junior with nickel laminations. The OT-2 (Paramour II and Paramount upgrade) is very similar, just different construction details. Unfortunately, at 3K primary impedance it also has the lowest turns ratio and with the 45 will have the lowest damping factor. Steel (M6 or M4) laminations are less costly and provide greater power handling (which you don't need for a 45), but they do not sound quite as sweet to my ears.
The Stereomour output (OT-3) is not currently offered by itself. At 4K it has a higher turns ratio so the damping would be a bit better. It's not made with a nickel core. I tried to get as close to the TFA-2004 performance as I could, in a smaller package with conventional materials and workmanship.
The EXO-45 has a 5K impedance and would have the highest damping factor. It's available with a nickel core, but also has the least power handling capability, so I would not use the nickel core option unless you were not going to push it in the deep bass.
The Robin Hood is also 5K; it's kind of an EXO-45 with a growth hormone problem. :^) Power handling is very high - if you can get Mike to make one with nickel laminations it will still be effortless in the deepest bass. It is the largest of them all, and might not fit inside the chassis.
For plate chokes, the Paramour II upgrade package included the BH-6 plate choke, 40 henries at 50mA. Even better for a 45 would be the SEX upgrade BH2, 50 henries at 40mA (different air gap, same number of turns. Failing that, the BCP-15 is very similar, and available with either air gap. Because plate chokes have many more turns, the core material distortion is attenuated and I would not bother with nickel, which would also seriously de-rate the current capability.
Hope that helps!
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Mine is close to Johns above. I use the BH-5 with a pair of EC-99's and I keep forgetting about the BCP-16 grid chokes. Gee we all can't seem to just follow instructions now can we;)
I replaced the input stage of the 6CM7 with a 12AT7 in an effort to get a bit more gain. I'm not sure it was worth it, there is more gain but I still can use a preamp in my somewhat low gain system and the 6CM7 is a pretty good sounding tube...John
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Hi Paul,
Yes, thank yu! This helps a lot. I don't see the TFA-2004 jr. on the MQ products page, but the other TFA-2004s look to be 3k , so is the jr. also 3k?
How deep do you mean by deep bass? My speaks do about 40 Hz and I don't use a sub. Thinking if exo-45 in pinstripe might work. Failing that, I'll most likely just go with the stock paramour II upgrade OPT. Also, my main source has a fairly low output Z and 2.25v rms output, so will I still need a preamp with my 95/96 dB speakers
If I wanted to raid my s.e.x. plate choke, and leave the nickel OPT, can I go back to the original s.e.x. plate choke, and what may the consequences be?
John, are you running yours full range?
Last night I found the paramour II product page and I didn't realize that these were the 8 x 10 format chassis. Can't wait to see if these have the upgrades or not.
-- Jim
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For what it's worth; I have Paramour I, with the SR45 upgrade PCB; but with the newer Power Transformer. This is the power transformer Doc does not have or can get anymore. I've use the BCP-15 for the Plate Choke, and Pin-stripped (nickle/M6) EXO45's for outputs. I works well for me. I use with DX3's in a large MLTL, and measured 101 dbSPL @1W.
As Elieen the Queen put it one time; I've squeeze all the performance out of an old Paramour I.
I'm glad to provide any notes I have.
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The Junior is the same winding, on a shorter stack of laminations (1.25" instead of 1.75"), so the impedance ratio is identical. Mike doesn't keep them in stock, but does a run every so often. The BH-5 is the same winding schedule, with different insulating materials. The leakage inductance and capacitance are both a bit smaller, so the high frequency performance is better. The power handling at low frequencies is reduced by the smaller core - not a problem with the 45.
Transformer cores are overloaded by excess voltage at low frequencies, independent of whether the speaker can reproduce those frequencies. Any overload distortion will intermodulate with sounds that are reproduced, you need to limit the low frequency power applied to the transformer to avoid this distortion. In the case of phonograph (and tape, with NAB eq) there is a built-in limitation, effectively a roll off below 50Hz. You can't always count on this with digital recordings, however. Additional protection is provided by the plate choke and parafeed capacitor, usually in the range of 10Hz-20Hz.
Sorry I'm unable to provide useful specific criteria. I am generally happy with a transformer that can provide the amplifier's rated power at 30Hz with 13000 Gauss of flux, using a M6 grain-oriented silicon steel core. The stock Paramour and Paramour II compromised on this, delivering full power down to around 60Hz, yet was satisfactory to a large majority of customers for many years. At the other end, many people prefer amps which can handle full power down to 20Hz or even 15Hz. For 50% nickel cores, you have to asses it at lower flux density, some use 8000 Gauss and others 10000 Gauss - about 40% and 60% as much power, respectively.
I have tried to balance the plate chokes and output transformers in our kits - a small transformer benefits from a small plate choke which gives a higher cutoff frequency, even though the other benefits of parafeed are reduced by a small choke. But swapping chokes is certainly practical as long as you are alert for the possible effects. The optimal parafeed capacitor value is proportional to the choke inductance, though I have adjusted the production value in some cases - most notably the stock Paramour where 1.25uF is optimal but I used 3.3uF - this deviated from optimum to provide a deeper bass cutoff frequency, at the price of potential transformer overload.
I suppose this muddied the waters more than clarifying things - sorry for that.
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Hi Paul,
Thanks, and yes this does help. It's not crystal clear, but not muddy either.
Elcraigo, thanks for the offer and info and I'll let you know when and if I need more help.
Actually, it seems as if all of this is moot for the time being anyway as there are no orders being taken at MQ, and I also suspect there are no more SR boards to be had.
-- Jim
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Jim, I do run mine full range. Most often with a pair of the Hornshoppe Horns. I sometimes add a sub but my Horns are well away from the corners and walls, so a little help in the bass doesn't hurt.
Paul mentioned new boards, which would be a help but the SR boards were not specific to the SR but were an existing C4S board with some component changes and jumpers...John
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would the PGP 8.1 PT work for the SR45 ?..... these are awesome amps....I also added the BCP-16 nickel grid chokes to mine ....and while probably not optimal, I dropped in a pair of EXO-36 cobalt OPT's for a listen verses the BH-5 nickel stripe OPT's..... sounded good to me
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The PGP8 puts out a lot more voltage, so the operating points would have to be revised significantly. It would still be the same amp, other than different resistors, capacitors, iron, power supply, and topology. :^) Haha
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Paul, you are so nice to take such a round-about way to say NO....wasn't there a 45 amp called the "single" that is similar to the SR45 where these PT would work?....I was digging around in some parts I have and came across some CP-06006 chokes (40 madc, 50 H, 550 ohms dcr) that look like a better fit for the SR45 from the info you spec'ed....maybe I can try those out soon
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There was an article called the "Simple 45" that was a 45 version of the circuit that John Tucker and I developed back on the late 90's for 2A3s. It does not use shunt regulation, and it was direct coupled with the active loaded driver tube sitting "under" the 45 tube. It was originally published in VALVE (which I hope to publicly archive on the Bottlehead site some day) and I believe it may currently be available through the Enjoy the Music website.
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I don't recall any amp called "single" - not that my memory is all that great! But we've only done the one fully shunt regulated amp, plus a one-off custom 2A3 amp which was quite a challenge.
The PGP8.1 can support a fully shunt regulated 45 design, possibly even one that is direct coupled. I'm just saying that I have not designed such an amp, and the PGP8.1 won't work with the amp(s) that I have already designed. The issue is mostly the voltage and power dissipation capability of available transistors in the current sources.
If I recall correctly (see memory comment above) the CP-06006 is essentially a prototype for the BH-2 plate choke used in the SEX amp upgrade package. It is perfectly suited for a 45. The starting point for several chokes was the BCP-15, 40 henries at 50mA. for the BH-2 it was re-gapped to give 50 henries at 40mA, and the internal construction was altered with superior materials and construction which are Magnequest proprietary. The same materials alteration with the original 50mA/40henry air gap, is the BH-6 plate choke in the Paramour upgrade package. Mike now offers your choice of air gaps on the BCP-15, so there are four current versions, all using variants of the same core and coil.
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Paul and others,
This is the amp that I asked about a couple weeks ago and has more information posted in the "My Next Project -- Tucker 45 monos" in the general discussion area.
So, who makes this CP06006 choke? That would be lovely for my SR45 -- if it's not a currently unobtanium MQ piece, that is.
Thanks,
Jim
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It's a Magnequest product, not listed. I think Mike only used that designation until we all agreed to call it a BH-2.
Mike said he would be out for a few months, so I kind of expect him to start taking orders again pretty soon. Right now I think he's snowed in with nearly two feet of snow in Philly ... :^)
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Paul,
Yes, a lot of the east coast was hammered. A couple feet of snow in Philly should bring things to a grinding halt for about a month :-). I grew up not far from Philly and that much snow is tantamount to a national disaster there.
-- Jim
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There was an article called the "Simple 45" that was a 45 version of the circuit that John Tucker and I developed back on the late 90's for 2A3s. It does not use shunt regulation, and it was direct coupled with the active loaded driver tube sitting "under" the 45 tube. It was originally published in VALVE (which I hope to publicly archive on the Bottlehead site some day) and I believe it may currently be available through the Enjoy the Music website.
It's on positive feedback:
http://www.positive-feedback.com/Issue1/single.htm
The article doesn't call it "Simple". I think that was a nickname it got later. Cool and "Simple" amps that sound very nice (I built a pair which I later dismantled to cannibalize some parts).
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Damn, just lost my post, I think if someone is replying while you are typing the forum drops yours, or something.
Anyway, I would like to build a SR-2A3, maybe using a 6V6 at the shunt tube. Paul, if you have any hints it would be appreciated. I often plug in a set of new 2A3
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John,
And I'm here in Boulder and it's 64 degrees and sunny out. We've had almost no snow at all this year, and temparatures more like Seattle area -- 40s/50s. I've been here 16 years now and this is by far the most bizarre winter we've had.
An SR 2a3 sounds lovely too.
-- Jim
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To make a SR 2A3 you need a minimum of 80mA supplying the shunt regulator - more is better. Regulated voltage will be (let's say) 380v. Allowing 5% compliance and another 20% for possible power line variations (+/-10%), the current source feeding the regulator must dissipate 9 watts, minimum. If your power supply voltage is a bit higher than optimum, it will be more. You can't reliably dissipate that much power with a TO-220 transistor unless you have a very large heat sink - around 10 cubic inches volume, and well ventilated for convection cooling. Incidentally, you must allow for the possibility that the mounting washer will fail, placing the heat sink at 400-500vDC, so it must be protected from accidental contact - without interfering with the ventilation.
That's an example of what I meant when I said "The issue is mostly the voltage and power dissipation capability of available transistors in the current sources" in a previous post in this thread. All these are solvable problems, but it would take a lot of engineering time to solve them in a safe and reliable way.
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It's on positive feedback:
http://www.positive-feedback.com/Issue1/single.htm
The URL is "...single" maybe that's how it got that name.
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Doc, Xcortes - that's the one...single / simple, looks like a nice 45 amp to build....thanks Paul for the history of the cp-06006....actually I think I bought those from Xcortes....Jim - you can not go wrong with the SR45...it is a fantastic amp....I switch between my 2A3 Horus w/ exo-36 cobalt OPT's (see the Magnequest site) and the SR45 and the SR45 every bit as good....
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awsjr,
Thanks for the note and another thumbs up for the SR45. The Horus has always been another of those amps that has caught my fancy, though I've never heard one, and from what I understand, the cobalt transformers are no longer available at all, so no need to worry about that. The SR45 should make a fine match for my office system, which is where I do my serious listening and where all the best gear endss up.
-- Jim