Ampeg J12-T

[Valvehead]

Looking at this J12-T and it has a minor issue (besides needing new tubes) , with the Intensity control on 0 , i can still hear the trem "pulsing" in the background . What would cause that signal to get through the pot if its at 0 ??

Leaky c30?

[g1]

Have you verified with your meter that 0 on the pot is 0 ohms?
Aside from that, the pulsing could be coupled through the power supply, C22 would be a suspect.

[Valvehead]

pot measures down to 47 ohms....ill replace it . Any sources for these odd pots --plastic 1/8" ?? shaft / knurled / ?? Ive seen these on Crates too


c21 is definitely bulging out the top ( 47uf/450v )

i need to pull the pcb so might as well do the filters--i think theres only 3 or 4
. Amp is dated 1995

EDIT-- found one =
https://www.fullcompass.com/prod/285...ot-for-svt4pro

[The Dude]

The pot should be this one:

https://www.fullcompass.com/prod/285...ot-for-svt4pro

[Valvehead]

The pot should be this one:

https://www.fullcompass.com/prod/285...ot-for-svt4pro

thanks--ordered !

[vintagekiki]

With wire short circuit TP5 and chassis (Tremolo off). If there is still a "pulsation" check C22; C23 (10uF / 400V)
Check on PCB that is no uncertain or cold solder defect in P4 (Intensity) circuit.

[Valvehead]

With wire short circuit TP5 and chassis (Tremolo off). If there is still a "pulsation" check C22; C23 (10uF / 400V)
Check on PCB that is no uncertain or cold solder defect in P4 (Intensity) circuit.

Its torn down right now. waiting on new filter caps and a pot. I did find a few questionable joints on the pcb