input capacitor?

[Steve Conner]

There is no 700 or 200Hz resonance because, as far as the pickup inductance is concerned, the input capacitor is in series with the Miller capacitance. 10nF in series with 100pF is pretty much equal to 100pF.

And as already pointed out, the other possible resonant mode is squashed by the grid leak resistor.

[Enzo]

Why would there be any DC at the input jack if the amp is wired properly?

Not from inside the amp. BUt pedals and other external devices with unterminated output caps will pop when switched in and out if you do not have a blocking cap.


Possible plate to grid short is not the reason for the cap, and I have never seen such a short in my 50+ years of electronics.