A friend who mistakenly thinks I'm smart, brought over a 4-tube Conrad Johnson PV3 pre-amp that is DOA. Filaments light up but all it puts out is a fairly loud mid-frequency roar, tried it with both the Boppers and the s/s Bedinis; Not 60 Hz, so no easy fix like an open ground.
My first guess was a bad tube but the channels are separately wired and the racket's the same on both channels and it does not pass an audio signal, so I'm guessing it's not a single lame tube and may be in the pwr supply or some other commonality. The caps all appear to be OK by visual inspection, though I've no real way to test them. The xformer looks OK, no bubbles. It uses 12XX7s in all four holes.
Might one of you be so kind as to steer me towards a diagnostic fix? Or should I just stuff it with new tubes?
Thanks
Dave
My first guess was a bad tube but the channels are separately wired and the racket's the same on both channels and it does not pass an audio signal, so I'm guessing it's not a single lame tube and may be in the pwr supply or some other commonality. The caps all appear to be OK by visual inspection, though I've no real way to test them. The xformer looks OK, no bubbles. It uses 12XX7s in all four holes.
Might one of you be so kind as to steer me towards a diagnostic fix? Or should I just stuff it with new tubes?
Thanks
Dave