Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: TurboGuitarMelton on December 31, 2020, 07:05:33 pm
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Hi,
Can someone help me understand what is going on with the V4 tube in this schematic? The .1uf cap to the .02 to .02 back to .1 doesn't make any sense to me. V4B looks like a typical amplification stage and then I see the 220k/15k divider. Is that to counteract the volume jump from the amplification stage? Would there be a way to add the trem in without adding this extra stage? Maybe make the trem interact with the V1B buffer stage?
Thanks
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Guitar signal is applied to V4B grid. Tremolo signal is applied to V4B cathode and modulates the cathode bias to vary the gain of V4B. So the guitar signal at the plate has been tremoloed. C13, C14, and C15, and associated resistors create a filter that passes the modulated guitar signal but rejects any remnants of the tremolo oscillator signal. The voltage divider knocks the signal back down to instrument level. V4A is a cathode follower/buffer/driver. The output signal is connected to the instrument input of another amp.
The circuit works fine as is. No need to try to reinvent it.
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> C13, C14, and C15, and associated resistors create a filter that passes the modulated guitar signal but rejects any remnants of the tremolo oscillator
I did "reinvent" that filter once. "This could be a lot better!" Tore didn't think much of my effort.
I agree it is fine the way it is. If I were forced to tamper, it would get chips in key places. The cathode followers are not "tone" just heat and tarnished sockets. Reverb recovery too. And the LFO is not "tone". And that cathode injection is about #5 on my list of good trem cells, behind optoresistors....
Leave it be.