Triode mode 6L6-oid is a great way to go. Also, you don't have to run UL for Mullard topology.
I might use a 6SN7 for the LTP and a 12AX7 for the input voltage amplifier. Triode-connected 6L6 for the outputs. I think I'd definitely prefer to use an LTP phase splitter for a 6L6. It's a little more complicated, though not by a ton, and can swing considerably more voltage compared to a concertina (cathodyne).
Edit:
If you're going to run triode mode, you definitely want to have a beefier tube like a 6SN7 to drive the higher miller capacitance of the output tubes.
I might use a 6SN7 for the LTP and a 12AX7 for the input voltage amplifier. Triode-connected 6L6 for the outputs. I think I'd definitely prefer to use an LTP phase splitter for a 6L6. It's a little more complicated, though not by a ton, and can swing considerably more voltage compared to a concertina (cathodyne).
Edit:
If you're going to run triode mode, you definitely want to have a beefier tube like a 6SN7 to drive the higher miller capacitance of the output tubes.
Original Poster:
I am not hearing enough about your desires about what you want in an amplifier.
The amp you build with Fisher 400 output transformers should depend on what you most want:
Max power
Simplicity
Low Distortion
Damping Factor
Stability with all loudspeakers
Easy to adjust and maintain
Power Draw from the Mains (environmental)
Frequency Response
Overall Finesse
Visual appeal of the output tubes
You can have some of the above, but not all of the above.
And, then what speakers do you have, your room, what music you like, how loud you like to play it?
Picking the output tubes requires knowing what you already have, and what you want.
I am not hearing enough about your desires about what you want in an amplifier.
The amp you build with Fisher 400 output transformers should depend on what you most want:
Max power
Simplicity
Low Distortion
Damping Factor
Stability with all loudspeakers
Easy to adjust and maintain
Power Draw from the Mains (environmental)
Frequency Response
Overall Finesse
Visual appeal of the output tubes
You can have some of the above, but not all of the above.
And, then what speakers do you have, your room, what music you like, how loud you like to play it?
Picking the output tubes requires knowing what you already have, and what you want.
Ok, so here's the deal: I have been in high end audio for 25 years (started last year of high school). All up and down the Naim line, Linn, etc. Now have Leben (first foray into tubes - NICE stuff . . . CS600 and the RS30EQ). BUT, BUT . . . the "hobby" has been less interesting lately, ironically as my income has risen and i realize I can pretty much afford whatever I want I lost a lot of interest. It's weird - but there's a certain sadness in this (honestly!!) and the hobby suffers. Anyway, my system sounds better than it ever has. And big whoop . . .
But THIS has been amazing!!! I bought my first vintage item about 8 weeks ago, I worked it over, watched a THOUSAND "Uncle Doug" and "BlueGlow" videos, have ACTUALLY learned something, and can spend six , EIGHT hours at my bench and hardly know where the time goes. I am 100% hooked. AMAZING hobby. And I don't seem to give two S*&%s if this stuff sounds as good as my Leben stuff (ha - I'm convinced it comes damned close anyway) - my Leben stuff has been sitting unused on a side board for 8 weeks!!!
I've got a Knight KN940A under my belt (failed); Shell 2020P (success, but could be improved) and Scott 299A (rousing success). And I have been buying cool looking stuff even if I don't know what kind of sound it will give. So, my next project is to build a bespoke integrated amp (probably line level) into a vintage and super cool chassis. I've chosen the Knight 93-320 as my donor chassis (I actually have two of these) - but will make a single stereo integrated.
I run vintage Tannoy Cheviots with HPD drivers (these runs 91 db sensitivity . . . the cheapest speakers I have ever owned, and they have changed my damned life) in a huge room. I never want for power - 15-20 watts per side is more than enough.
My priorities are these in this order:
1) A successful built. Done in a "craftman's" style (see the Uncle Doug's video on Youtube of the WE Grable Amplifier to see what I aspire to. . .
2) 20 watts per channel is the sweet spot. More or less. . .
3) Should not sound ****. That says pretty much all I know how to say about damping factor, distortion and frequency response.
I WILL say this - I have never been a fan of the "tubes sticking out of block" look. I don't mind the look of tubes, but I always like the look of a tube cage better (unless its that abomination that Prima Luna uses), But my overwhelming preference is an enclosed chassis (like my Leben stuff) or casework. I think the late 40's/early 50's "Industrial" look of the Knight 93-320 is spot on for what I have in mind.
IF I pull this off, I look forward to doing a more ambitious project in what I consider to be a super cool Rauland PA amp Model 1932 from the 40's (I have one in AMAZING cosmetic condition. And it's HUGE, so I can do what I need. I have some super cool vintage TOBE "Oilmite" capacitor cans which till have the paper on them that I intend to re-stuff and use for THAT project. But baby steps.
So, that's my plan.
But THIS has been amazing!!! I bought my first vintage item about 8 weeks ago, I worked it over, watched a THOUSAND "Uncle Doug" and "BlueGlow" videos, have ACTUALLY learned something, and can spend six , EIGHT hours at my bench and hardly know where the time goes. I am 100% hooked. AMAZING hobby. And I don't seem to give two S*&%s if this stuff sounds as good as my Leben stuff (ha - I'm convinced it comes damned close anyway) - my Leben stuff has been sitting unused on a side board for 8 weeks!!!
I've got a Knight KN940A under my belt (failed); Shell 2020P (success, but could be improved) and Scott 299A (rousing success). And I have been buying cool looking stuff even if I don't know what kind of sound it will give. So, my next project is to build a bespoke integrated amp (probably line level) into a vintage and super cool chassis. I've chosen the Knight 93-320 as my donor chassis (I actually have two of these) - but will make a single stereo integrated.
I run vintage Tannoy Cheviots with HPD drivers (these runs 91 db sensitivity . . . the cheapest speakers I have ever owned, and they have changed my damned life) in a huge room. I never want for power - 15-20 watts per side is more than enough.
My priorities are these in this order:
1) A successful built. Done in a "craftman's" style (see the Uncle Doug's video on Youtube of the WE Grable Amplifier to see what I aspire to. . .
2) 20 watts per channel is the sweet spot. More or less. . .
3) Should not sound ****. That says pretty much all I know how to say about damping factor, distortion and frequency response.
I WILL say this - I have never been a fan of the "tubes sticking out of block" look. I don't mind the look of tubes, but I always like the look of a tube cage better (unless its that abomination that Prima Luna uses), But my overwhelming preference is an enclosed chassis (like my Leben stuff) or casework. I think the late 40's/early 50's "Industrial" look of the Knight 93-320 is spot on for what I have in mind.
IF I pull this off, I look forward to doing a more ambitious project in what I consider to be a super cool Rauland PA amp Model 1932 from the 40's (I have one in AMAZING cosmetic condition. And it's HUGE, so I can do what I need. I have some super cool vintage TOBE "Oilmite" capacitor cans which till have the paper on them that I intend to re-stuff and use for THAT project. But baby steps.
So, that's my plan.
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It sounds like the physical size of the tubes will be a consideration (so probably no 807s), but at some point there is really no "right" choice of output tube, and just a few "good options", and you have to decide what you want to use. As much as you can dig deep into the minimal advantages and disadvantages of the various options that will work with your transformers, the bottom line is that you can build an *excellent* amp around either.
How much are you worried about the cost of tubes? From your post it doesn't sound like you're too concerned, but I don't want to make any assumptions. 7591s tend to be more pricey than 6L6s, and you don't have the less expensive Russian versions like you do with the 6L6.
How much are you worried about the cost of tubes? From your post it doesn't sound like you're too concerned, but I don't want to make any assumptions. 7591s tend to be more pricey than 6L6s, and you don't have the less expensive Russian versions like you do with the 6L6.
PROBLEM SOLVED!! I have happened across a “Knight Basic 60 Watt Amplifier. This is coming complete with Mullard EL-37’s. I am told this is essentially the Mullard 5-20 circuit and can be built with 6L6GC. Which seems reasonable. IF I decide to actually use these Millard’s, I’ll probably build it into my Rauland chassis which will show off the tubes, choke and big TOBE cans better.
Looking at the data sheets for the 7591 there doesn’t seem to be any kink below 100 volts plate at low current, like the 6L6 and all the bigger ones seem to have. Would that tend to make it more well behaved than a 6L6 at high Ra loads? Was it a selling point back in the day? Or does it get just as kinky at Vg below -16 (where the curves stop)?
wg_ski,
Good point!
Push Pull transformers have lots of primary inductance.
So a high QMs woofer might be a problem with a kinky tube.
However,
Single Ended transformers do not have nearly as much inductance.
The plate current can not go low at low frequencies,
and so might not push you into the kink.
"All Generalizations have exceptions" - Me
Good point!
Push Pull transformers have lots of primary inductance.
So a high QMs woofer might be a problem with a kinky tube.
However,
Single Ended transformers do not have nearly as much inductance.
The plate current can not go low at low frequencies,
and so might not push you into the kink.
"All Generalizations have exceptions" - Me
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I wouldn't design a new circuit around EL37s. They aren't too easy to find, so future maintenance could be an issue when they get even rarer.
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