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Video of noise when I switch on the reverb of my Twin Amp

tochiro

Member
Messages
2,631
Hi,

Here is a video of me switching on and off the reverb of my Twin Amp:




The amp is only 4 years old and in very good condition, tubes are new and correctly biased, apart from the noise the reverb is working normally.

Do you experience the same problem?

Thank you.
 

famouspogs

Member
Messages
472
I had a Twin-amp that would ALWAYS go microphonic with the reverb regardless what tube was in it. I've never heard that though, it sound's like one of the reverb cables has been damaged or pulled out from the reverb tank. You've probably already checked that though I imagine.
 

Braciola

Gold Supporting Member
Messages
6,273
Sounds like one of the reverb cables isn't making a good ground connection.
 

tochiro

Member
Messages
2,631
Yes I checked the reverb cables and they are ok :-(

I should add that the tremolo is producing the same kind of hum with the modulation on top of it.
 

The_Whale

Member
Messages
6,133
Does the noise get louder when you turn up the reverb?

Is there a reverb on/off switch for the different channels in the back of the amp? What does the noise do when the footswitch is disconnected?
 

tochiro

Member
Messages
2,631
Yes, the noise gets louder when I turn up the reverb. In my video, the reverb was at 6 (of 10 graduations) and all volume at 0. There is no on/off switch at the back of the amp. The noise remains the same if I disconnect the footswitch.
 

StompBoxBlues

Member
Messages
20,102
Is the reverb tube driven? I would check the tube (preamp) for reverb if so. Trade it out with a known good.

If you touch the reverb tank, does the sound change?
 

tochiro

Member
Messages
2,631
Yes the reverb is tube driven. I changed it recently for a new tube but to no avail. No sound change if I touch the reverb tank.
 

StompBoxBlues

Member
Messages
20,102
Was there any change at all when you changed out the preamp tube?
I'm just throwing things out here, for one thing it sounds a little like 60 hz hum, like from power.

I think (it's hard to see) that I see your video has the guitar going into pedals then into the amp when you do this.

Does it still do it when nothing is plugged into the amp (not even guitar I mean)? Does it sound the same with even just guitar plugged in?

WHEN did the sound first appear? Was it right after changing tubes you mentioned?

Oh yeah, another thing...is it possible the footswitch is doing it? Either something wrong in there, or the cable? Can you turn the reverb on and off without the footswitch attached?

What I'm getting at is just try to simplify (leas amount of variables), and also try to change the sound..does it change if you move the footswitch or FS cables? etc.
 

tochiro

Member
Messages
2,631
Thank you for your time StomBoxBlues. It sounds exactly the same with nothing connected to the amp. Even with the footswitch disconnected. There was no change when I changed the tubes. I do not remember when I first noticed it or if this problem happened progressively but I think it happened progressively. To sump up, this hum stays exactly the same whatever is connected to the amp. The only variable is the reverb volume.
 

StompBoxBlues

Member
Messages
20,102
Thank you for your time StomBoxBlues. It sounds exactly the same with nothing connected to the amp. Even with the footswitch disconnected. There was no change when I changed the tubes. I do not remember when I first noticed it or if this problem happened progressively but I think it happened progressively. To sump up, this hum stays exactly the same whatever is connected to the amp. The only variable is the reverb volume.
Hmm... I don't know for sure if this is easy to do on this amp, but
I was wondering, how are the reverb cables connected to the reverb unit?
What I mean is if it is easy to disconnect them on the amp side (not the reverb unit side)... to try and isolate if the problem is in the amp or in the reverb unit itself? Not even really sure if it wouldn't make noise if disconnected and working okay...so really...

It sounds like you have done a lot but that it might be time to take it in to a repair place. Most likely an easy fix. If you still had the old preamp tubes (all of them) I would probably try putting them back in...but it is just a shot.

Maybe there is a filter cap that went bad that would filter any AC to ground, not really sure, but even if so, would probably need a service person to do it.

It was smart of you to make the video though! Did you try posting this in the other TGP forum (amp technical?)...some very experienced folk there maybe have some more useful than I have been able to give...

Good luck!
 

DT7

Member
Messages
2,794
You know, it might be as simple as the lead dress. The wiring for both the reverb and tremolo pots pass very close to the B+ filtering lines. You might want to pull the chassis and check to see if moving them away a bit changes anything.
 






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