This is VERY, VERY rare so listen up. Two tales from the crypt...
Tale Number 1
It was dark one night .. and I was building a Tweed Deluxe. I was having all sort of problems on the normal channel with noise, crackle, DC on the input jacks. I had practically replaced everything.
To make a very long, frustrating story short, it was a
slightly conductive Ceramic tube socket!! One of the pins somehow had a few Meg to ground.
It should be Zero, 0, nothing, nadda.
Now I test the pins to be sure before I install them. One probe on the ceramic and I touch each pin.
Never seen this before, ever, with a new socket.
Tale Number 2
It was dark one night .. and I was building a TMB and the lightning was flashing outside.
I was having all sort of problems on both channels with noise, crackle, DC on the input jacks. I had practically replaced ot tested everything. I was at a total loss. A midnight call to Doc Martin did nothing to resolve the problem. The plot thickened...
To make a long, very scary story short, it was a
slightly conductive Turret Board. I accidentally discovered it when testing voltages. 50 VDC from an unused turret to ground. Ouch!
It should be Zero, 0, nothing, nadda.
Never ever, ever seen this before nor had anyone I talked to including the Holy Ghost. I replaced & rebuilt the board and the problem was fixed.
Needless to say, I quickly changed suppliers!!