Fender CBS Pro Reverb Master vol - :Normal channl reverb bleed thru

[g1]

I know I will be listening for the issue all the time now.

[Helmholtz]

I learned something about my Fender amps, too. So I'm grateful.
I've been using Fender reverb amps (almost exclusively) since 1980.
But as - like most players - I always use the vibrato channel (I love a little reverb, don't care about vibrato/tremolo), so I didn't notice the "issue"-.

[Chuck H]

A shared 250µ cathode cap would lower the unwanted signal by a factor 10 or 20dB.

I tried that at the time in the simulation too. Actually a 220u cap at as new spec for ESR. And you're spot on. With only 50mV drive at the reverb power tube grid I don't think it would be an issue. And I checked on the amps signal frequency analysis just to be sure the really high value cap for that application wouldn't mess with the amps tonality and it doesn't. No change (well, less than three tenths of a dB at 80Hz) at audible freqiencies and only 2dB at 20Hz.