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In Reply to: RE: WESTERN ELECTRIC 91A CLONE DISCUSSION posted by maxhifi on November 21, 2014 at 14:34:16
Have you seen the 91A project from Sound Practices magazine? (Issue #1 summer 1992) It's a very nice sounding amplifier based on the original WE 91A. I think the article will answer most of your questions and also includes a schematic.
Follow Ups:
Some time ago, I made up a parafeed version derived from the SP article using Magnequest iron, and posted it on Mike's forum (Magnequest Mike is a friend). I made as few changes from Joe's article as I could, trying to keep the sonic as close to Joe's as possible but with modern Magnequest iron. I'll link the thread below in case anyone is interested. The usual - anyone is free to make your own variations or copy, I'll be unhappy if you pass this off as your own or make a bunch of money without a prior agreement.
It looks like I never posted the actual circuit, just emailed it to a few people. But I'll post it here if there is some interest, along with my design notes.
Paul,
How tapped out is the power transformer for filament current? Say I would like to drive a pair of EML 300B mesh plates which draw 1.5 Amps, can this circuit support that within 5% or should I consider a separate filament transformer? If a different transformer, can you recommend one (at least voltage and current) that would work with the FT-1 and support 1.2 to 1.5 Amp draw?
Thanks,
Aaron
Hope yo don't mind me letting folks know exactly where.
Thanks for your ongoing contributions.
Cheers.
"In the beginner's mind there are many possibilities, in the expert's mind there are few." Shunryo Suzuki
I thought I had but was looking in the wrong place.
There is interest here! Would love to see your adaptation Paul.
I read the sound practices article before posting here, however I don't feel as though all stones are unturned yet. Several years ago I built a 2A3 and EF37a amplifier, and I feel like I took too many shortcuts to really get the point of the whole single ended triode thing. This time I want to do it right.
There is more complete information about this on the Web, but I lost the URL. Maybe someone can help out?By the way, it will take any 2.5K OPT from Magnequest, like the DS-025.
Observe, before you think. Think before you open your yap. Act on the basis of experience.
Edits: 11/21/14
Frihed89:In 1947, Jack Robin and Chester Lipman published a small $2.00 book entitled “Practical Amplifier Designs”, sub-titled “45 Proven Circuits for the Technician and Experimenter “. One of their circuits in this book actually was a two stage direct coupled (6SF5 - 6B4G) all triode amp shown by you in this thread, and probably similar to the “Fi” amps of today .
A couple decades later, I imagine Asano and Shishido were obviously privy to that book and schematic you posted.
The Serious Stereo amp is somewhat different.
Topology wise, it does NOT take the B+ for the driver tube from the top of the Final's tube cathode. ( Not stabilized and too low in VDC ). No, not at all. It uses a R/C network off of the main B+, a slightly higher B+, and feeds the front end tube from a "cleaner" and higher B+, a R-Dropper you may call it. Dennis voltage choices and op points are ideal for highest fidelity and longevity.
Additionally, unlike many a DC amp I have seen, Dennis employs a simple shunt regulator, a no feedback type, such that it lowers the Z of the driver supply to wonderful levels. This gives his amps a GREAT low end, and stabilizes the mu of 100 driver tube, advantageously. So, the driver stage is totally shunt regulated, unflappable, and has a mVAC content of under 2 mVAC !!
Then, there are other DF topology audio circuit tweeks that I am not at privy and hesitant to discuss, but very very effective from my experimenting with them.
Dennis, in my experience, has the "most perfect" topology and execution of any of these DC amps I have studied, by far. And I am not just talking about his B+ filtering to the finals, LSES !!!
Just A-B Dennis' DC 2A3 amps, particularly his latest ones !!!, with ANY other DC amp. That tells the tale. Lakerfan uses a mildly-updated early DF amp, and reported what he hears to us - and he claims he has owned 50 SETS !!
Jeff Medwin
Edits: 11/22/14 11/22/14
set up a separate SS forum or a DC 2a3 forum and spare us.
Hi Jeff.I know you mean well, and like what you hear, but all I wanted to do in the first place was to contribute something useful to the guys here.
What I didn't want was for me or my equipment to become a "Hot Topic" discussion item.
Everyone on here has the right to his own favorite topology, and right or wrong, ordinary-sounding or not, he also has the right to believe in it.
In fact, believing in what one is doing is a key step towards improving anything, so give these guys a break.
I don't wish for this "praise-to-the-moon", and then "kick-to-the-Gutter", "scientific", then "non-scientific" cycle to persist any longer--it's not useful to forum members, many of whom are plenty smart enough to understand both camps..
The Flame-Outs are getting increasingly psychotic to say the least-- even to the point of denying the common IEC socket wiring topology that EVERYBODY uses!.
Let's all return to reality and common decency and do things objectively, and show due respect for different apps, methods, and listening preferences..
---Dennis---
Edits: 11/22/14
OK, will do and co operate. Cheers !!
Jeff Medwin
Please keep the craziness in the crazy thread below. This thread doesn't need it.
Get a room...separate forum. did Gusser not say he stands corrected regarding IEC as you acknowledged you could not see it was properly connected in the photo. He did not "deny" something common. Has Don Garber been around this forum shilling?
Edits: 11/22/14
Moving forward would be not to bash or slight another design.
Someone on one side of this conflict has recognised that the bickering needs to stop. There is a small prospect of improved relations; maybe even civility, heaven forbid.
To both sides: if you simply can't let it go and move on, let us know what outcome you would like from this petty conflict and how - perhaps with our help - you are going to achieve it. But really, trying to square a ledger of past grievances rarely in my experience delivers productive outcomes for either side of a conflict. It is currently rather miserable - move forward.
Act like the intelligent professionals you claim to be.
Cheers.
"In the beginner's mind there are many possibilities, in the expert's mind there are few." Shunryo Suzuki
After all the discussions below must we still endure this in every thread here?
The reference is below. The amp is on pp. 6 and 7.
Observe, before you think. Think before you open your yap. Act on the basis of experience.
This looks loke a loftin white variant. The 6SF5 is more or less half a 12AX7. I think the down side to this circuit is it needs a huge B+ voltage. Never heard one but it sure looks elegant ... I have some old Color TV power transformers which would be ideal for this circuit .
Google on "Don Garber Fi 2A3 monoblocks" and you'll get an idea of what a slightly modified version of this circuit looks like. I believe that this circuit is also the basis for Serious Stereo 2A3 SET built by Tube Wrangler, which operates at much lower power out than the Fi Audio build.
I have heard the Fi version. (I own one). I'm not sure if it's the AVVT meshplates or the design that makes it sound so good, probably both.
Observe, before you think. Think before you open your yap. Act on the basis of experience.
I've heard the DIY HiFi Supply WE-91 clone kit at RMAF in Denver some years back and must admit, to my taste in tube amp, it hit the spot.
6Moon Review: http://www.6moons.com/audioreviews/diyhifisupply2/max.html
Link below: More info from one who contributed to the design(or improved on it).
This one looks like one of the most interesting of all from the description, perhaps the truest to the original but unfortunately none of the images work anymore... if anyone would happen to have a schematic of his amplifier I would be very happy to see it.
Note: the amplifier in the photo doesn't appear to be the design he is talking about in his post, that nine pin miniature tube isn't part of the 91A design
But not the one I heard at RMAF, which was DIY HiFi Supply's original take on the WE 91A.
I have the DIY HiFi Supply original 'Billies' which use a 6SL7 SRPP to drive the 300B. I do plan a rebuild soon, as these amps are now over 10 years old. Best case would be to find the schematic for the original DIY HiFI WE 91 SET version and do a major upgrade, as I have heard this amp compared to mine in the same room at RMAF and clearly prefer the sound of the WE91 version.
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