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FDP Forum / Amp Mods, Repairs, and Projects / Twin Reverb crackling noise issues


USA / San Jose

Dec 12th, 2016 01:38 AM   Edit   Profile   Print Topic   Search Topic


I have a Twin Reverb amp and the issue I'm having is with loud crackling sound that it makes quite frequently. This is mostly with the Reverb turned on.

This is not a consistent issue, and it can work for hours w/out issues and then it starts again.

I had a local shop re-tube it an set bias, but still have not solved.

Did anyone have issues like mine - what can this be?


Thank you!

Contributing Member

So. Cal. USA

Dec 12th, 2016 09:41 AM   Edit   Profile   Print Topic   Search Topic

Black face circuits sound this way when the grid/plate resistors begin to fail on the preamp tubes. I change the slope resistors also when I do these.

Could be other things but check resistance with a DVOM. You can read these in circuit. If testing hot for DC voltage use caution and keep one hand in your pocket!

I just copied your urls. It's a Twin Amp, not a Twin Reverb. The above still applies however with the channel switching and other goodies they have in this amp you could have a bad relay or switch causing this as well. Many more possibilities with the Twin Amp compared to the TR.


USA / San Jose

Dec 15th, 2016 01:28 PM   Edit   Profile   Print Topic   Search Topic

Great- thank you, Hammond101!

Will try making these enhancements.




Jan 16th, 2017 05:48 AM   Edit   Profile   Print Topic   Search Topic

Hello kronrod,

Any update on this?
I started to have the same issue on my Twin Amp.


Steve Dallman
Contributing Member

Merrill, Wisconsin

Age is just a number...mine is big
Jan 18th, 2017 06:28 AM   Edit   Profile   Print Topic   Search Topic

I just chased such a crackling noise in my 65 Princeton Reverb.

It was a broken ground on the brass strip, under the controls. This is common and I actually feel a little foolish not finding it sooner. 15 years ago, it would have been the first place I'd look.



Jan 23rd, 2017 03:13 PM   Edit   Profile   Print Topic   Search Topic

Here is a video:



Jan 24th, 2017 02:27 AM   Edit   Profile   Print Topic   Search Topic

That's interesting - it seems as if the noise is being 'reverbed'.
So the noisy circuit is likely in/prior to the driver stage, rather than the recovery stage.

Can the noise be detected in the background with the reverb turned to minimum, eg with presence turned to max?
Does switching the fx loop in/out affect the noise? Turn send and return level controls to max.
Is the noise affected by which power mode the amp is set to?
Does the noise stop if the amp is operated without a tube (12AT7) in V7?

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