Hot Rod Deville squealing

[craigslee]

Hi guys,

I have an issue where I have a high pitched squealing occurring in the "more drive" channel as I increase the gain, treble or middle. (pretty much anywhere past half way)

I have found that, with the back panel off, the squeal will disappear completley when I place my finger on the ribbon cable of the second preamp valve.

The issue is not evident in the 2nd input. Just the 1st input. (higher gain?)

Can anyone explain why this is the case?

P.S. I have just replaced all my preamp valves with new JJ's. It still happens.

Thanks in advance.

[jaysg]

As a quick test, get a good 20uF/500V cap and start tacking it in across the PS caps.

[craigslee]

Thanks for the tip jaysg. Will try that.