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Finally used these Mullard reissue EL34s in a SE UL amp with 3.5K 10W OPTs and external PS. Rec tube is a Sylvania 5U4GB and driver tube a Tung-Sol ECC803S gold pin but any 12A*7 can be rolled here. Also 6L6 and KT88s can be rolled as power tubes. Power tranni is an over specced Hammond and the amp steel chassis is Hammond also.http://retro-thermionic.blogspot.com/2024/11/perspective-el34-single-end-ultra.html
| retro-thermionic |
Edits: 11/19/24 11/19/24 11/19/24Follow Ups:
You really should consider optimizing the circuit for a particular 12A*7 tube. The operating points are quite different between a 12AX, 12AU, 12AT and 12AY. That can have a big effect on gain, distortion and how well the tube can drive the power tube.
If it were me I'd likely try to use the 12AT7. Its got more guts than a 12AX7 and is often used for driving power tubes. The extra gain could be used for feedback since this amp likely sounds fine without any at all; the feedback would allow the amp to drive a wider range of speakers with flatter frequency response. And a greater amount of usable power. If you mix the feedback with the incoming audio using a divider network rather than applying it to the cathode you'll find it doesn't have the ill qualities so many people say feedback has.
Is a schematic forthcoming?
The front end was engineer designed to work with a broad range of tubes. No optimising intended or required. This is a tube rollers dream amp. The front end originally designed for 6N1P. I replaced it with a universal (4SU) frontend. My other EL34/6L6/KT88 amps all use 12AT7s not by design but by choice. Great tube in my 6L6 amps but here the upmarket Tung-Sol gets a place. Also I have Lin Lai 12AU7s to drop in. Universal design allows me to do this without fuss.
| retro-thermionic |
nada aqui
I used a self modified version of this with 4SU frontend to use a Tung-Sol ECC803S gold pin I had onhand.
| retro-thermionic |
Edits: 11/20/24 11/20/24
"any 12A*7 can be rolled here"
In a circuit designed for a 12ax7 a 12at7 or a 12au7 would not perform properly without adjusting the circuit values. There are large differences in mu, plate resistance and transconductance between those three tubes.
I've always wondered why people contend that a circuit can use multiple different tubes without modification?
That belies the facts.
By the way, nice looking amp.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
No tube is optimised but all tubes work well.
| retro-thermionic |
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