volume change by it's own

[JC@]

I have an amp here, and the owner says that sometimes while playing through it it goes very loud, then comes down again. Without touching anything of course.

I asked if it sounded distorted when it jumped loud, but he says no.

So here I am a bit puzzled. Any input here?
Merry Christmas.

[Alex R]

Number one suspect is the effects loop of course... see if jumpering it with a lead cures it... sorry if you already did that!

[JC@]

Number one suspect is the effects loop of course... see if jumpering it with a lead cures it... sorry if you already did that!

This amp is a 4 x 6l6 fender clone, not sure about the model.
Reverb and vibrato, no effects loop.
As I was told, the problem is that while playing, suddenly the volume jumps up very high. While I was working on it to solve other issues like bypass caps, volume pots and something else needed, I havenīt been able to reproduce the problem on the bench.
The owner told me that the preamp tubes are all new, and the problem was there even before the tube change.

[Bruce / Mission Amps]

Since the amp is a Fender clone with vibrato I'll assume it has an LDR vibrato circuit... if that cell goes bad and or the light gets stuck on, the resistance to ground at a critical preamp stage will be very low shunting a huge amount of signal to ground before it can get to the phase inverter.
So I'd check around on the board in that area very well too.

[JC@]

Bruce, thanks for your input.
I just sent a message to the owner asking if the vibrato was activated when this happened, but if I remember right he told me before that it happened on both channels..

[JC@]

Bruce, I just received an answer from the owner.
Yes, he doesnīt use a pedal to turn the "vibrato" ON and OFF, he just turns both controls down, so there's the problem, the neon sometimes goes on.

He just "remembered" that he has to turn the volume up to mantain the loudness to normal, so when the neon lights up the volume goes to a real normal level.

Fiuuu. Silly customers.

Conclusion: it is better to use a pedal switch to turn the vibrato on and off.