One for the techs - vintage Fender amp issue

Ossyrocks

Hi chaps,

My amp is currently with a friend having a little service. It's a 1965 Deluxe Reverb. It was humming badly, so the mains filter caps have been done and that fixed the issue.

The Normal channel is fine but he's a bit worried about signal still being passed through the amp with the Bright channel volume set at zero and thinks it could be another leaky cap or maybe a bad resister. 

I don't want to be changing out caps and resisters without good cause. What do you think? @ICBM ?

Cheers,
Rob.

RiftAmps

Ossyrocks said:

Hi chaps,

My amp is currently with a friend having a little service. It's a 1965 Deluxe Reverb. It was humming badly, so the mains filter caps have been done and that fixed the issue.

The Normal channel is fine but he's a bit worried about signal still being passed through the amp with the Bright channel volume set at zero and thinks it could be another leaky cap or maybe a bad resister. 

I don't want to be changing out caps and resisters without good cause. What do you think? @ICBM ?

Cheers,
Rob.

It's usually the pot itself, swap out for a CTS A1M or similar if it annoys you. Alpha A1Ms do this from new.

Ossyrocks

RiftAmps said:

Ossyrocks said:

Hi chaps,

My amp is currently with a friend having a little service. It's a 1965 Deluxe Reverb. It was humming badly, so the mains filter caps have been done and that fixed the issue.

The Normal channel is fine but he's a bit worried about signal still being passed through the amp with the Bright channel volume set at zero and thinks it could be another leaky cap or maybe a bad resister. 

I don't want to be changing out caps and resisters without good cause. What do you think? @ICBM ?

Cheers,
Rob.

It's usually the pot itself, swap out for a CTS A1M or similar if it annoys you. Alpha A1Ms do this from new.

Cheers for that.

If it's the pot itself, then the tone of the amp will not be compromised by this "fault" right? So if I can live with it, there's no harm in leaving it alone?

Rob.

ICBM

Check the grounding of the brass strip along behind the pots - it frequently cracks the solder joints to the chassis. The symptom of this is signal leaking through when the volume pot is on zero but going quiet when it's up a little, because the second gain stages share a common cathode network on the preamp valves and the channels are out of phase, so the signals then cancel out.

I don't try to re-solder the cracked joint - which would nee a hugely powerful iron - I run a new ground wire from one of the pot ground connections to one of the existing ground points, usually from the intensity control to where the bias supply is grounded... but you may have to experiment to find the place with the lowest noise.