Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: leevc5 on August 29, 2026, 08:56:49 pm
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Yes, I just finished my first PR build and it turned out great with some help from you people. It now belongs to a friend of mine who more than deserves it. So, decided to build myself one but have no need for tremolo so left it out. My plan was that would be able to find some usable circuit to fill the void has not come to pass.
So, here I am again hoping for some guidance.
Any suggestion is not too wild as long as it doesn’t involve adding opamps or any sort of digital noise makers.
I bought the components from Hoffman. The transformers I already had. Used the aa1164 circuit schematic and layout.
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You could shift all the socket wiring across one step, so instead of V4a being free it would be V1a that is free, and have an optional front gain stage, a bit like the Marshall 2203 with a "High/Low Sensitivity" input system,
Marshall biased that V1a stage with higher values for their crunchier thing they do, but you could leave it with stock Fender values or lower to get a more suitable milder smoother gain level for a Princeton.
Or if you do home recording a cathode follower line level output could be build from one 12AX7 section, to run to a computer interface / mixing desk / PA system etc
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Alternatively, you could do a one-tube reverb and only use three preamp tubes, so you wouldn't have an extra triode left.
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There's no shame in having an unused triode in an amp. Fender has plenty examples.
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This is a poor man's FX loop in a basic 'one channel AB763', but you could stick the same idea in a PR with 1 12AX7 triode - with a bit of imagination
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Another alternative would be to use a mosfet for the cathodyne, and get rid of that whole V4 valve.
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Convert SLPI to LTPI. Sounds better, adds some overall gain.
--Pete
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You could switch to a 7-pin socket and use 6AV6 (like a single 12AX7-triode) or 6AT6 (like a single 5751-triode).
Now there is no "extra triode" to use up. And NOS-prices are very cheap compared to 12AX7s.
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Convert SLPI to LTPI. Sounds better, adds some overall gain.
--Pete
Quite a lot of extra gain to be dealing with, typically around 25-30dB, almost equivalent to an typical additional common cathode gain stage.
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Quite a lot of extra gain to be dealing with, typically around 25-30dB, almost equivalent to an typical additional common cathode gain stage.
That!
Would result in huge NFB and instability.
(BTW, LTPI gain is 50% of a "bypassed" common cathode gain stage with same tube.)
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Convert SLPI to LTPI. Sounds better, adds some overall gain.
--Pete
Quite a lot of extra gain to be dealing with, typically around 25-30dB, almost equivalent to an typical additional common cathode gain stage.
Actually about 1/2 that of a typical 12AX7 bypassed.
--Pete
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Actually about 1/2 that of a typical 12AX7 bypassed.
See post above.
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Actually about 1/2 that of a typical 12AX7 bypassed.
See post above.
yeah i missed that.
--pete