J5mk1_problem volum knob

speedfender

hello, I made a J5mk1 amp last few years, but I have a problem whith, since I did it.
When I turn the volume up boutton with guitar pluged, the sound whistles.

Demonstration :

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What can I do ? the problem is not with the potentiometer, I have changed.

Sorry for my English,
Thanx for all.

Dejan

Hi,

You can check several things:
1. Wires layout - try to move around wires around the the first preamp tube (with eg wooden chopstick) with amp on and volume on max (see if that affect squeling)
2. Check grounding - conections, soldering points
3. Try to swap preamp tubes - one can be microphonic
4. Double- check all wiring/conections

If none of this helps, try 'band-aid' solution - connect capacitor of 1nF or less (250V) between the plate and cathode of the first gain stage. If squeling still exists, add another cap to the second stage.

1nF at the first gain stage solved the problem for me, with no (noticable) effect on the sound

Good luck
Dejan

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