I am working on an AMC CVT-2030 which was a low budget hybrid EL34 PP amp that I got for basically nothing. Yes, the one with the output tubes soldered in. I have put in tube sockets and used a holesaw on the heat sinks to make room. I can't find a schematic for this model but there is one for the CVT3030 which is basically the same thing with a preamp. My question is about the value of the coupling cap from the drain of the driver MOSFET to the grid of the EL34. The value in the 2030 is .1\250v film. The 3030 is a 1u\250v electrolytic. I have very limited theory and design skills, is there a formula to calculate optimum values for grid coupling caps?
Resistor/capacitor (RC) combinations form filters. A coupling cap. combines with the grid to ground resistor to form a high pass filter, whose slope is 6 dB./octave. The formula for RC filters follows immediately.
(2Π) (F3 dB. down {in hertz}) (R {in Ω}) (C {in farads}) = 1
Acquiring some theory is essential. A number of excellent texts, including the 1st or 2nd edition of "Basic Electronics for Scientists" by James Brophy, are available. Also, NEETS, which is U.S. Navy training materials, is available gratis on the WWW.