Question about my 1965 Twin

David Cook · Post by **David Cook** » 4 Feb 2023 4:08 pm

Yesterday my Twin worked fine for about 10 minutes then started having the low volume white noise that I could almost live with.
Today, it was fine for 10 minutes and then had a very loud white noise incident lasting 3 seconds and then was fine for 2 minutes and then didi it again very loudly
If I slap the top it will stop for a little then start again
Any thoughts?
Thanks

Raybob Bowman · Post by **Raybob Bowman** » 4 Feb 2023 7:52 pm

Sounds like old filter caps. If they are over 20 years old, I would think time for new filter caps and bias cap.

Dan Beller-McKenna · Post by **Dan Beller-McKenna** » 5 Feb 2023 3:36 am

That was my first thought. Happened with my LTD. New caps solved it.

Dave Grafe · Post by **Dave Grafe** » 5 Feb 2023 4:00 am

99% of tube amp issues are about tubes. Before opening up your amp and changing stuff replace tubes, preferably one at a time to isolate the problem. Bad caps generate hum not hiss, and sometimes no noise at but simply reduced plate voltage, resulting in increased distortion, and while new caps in an old amp is a very good idea it doesn't sound like that is your current issue.

Dan Beller-McKenna · Post by **Dan Beller-McKenna** » 5 Feb 2023 4:10 am

That's good advice, Dave. And tubes could be the culprit. As it happens, my bad caps produced a white-noise, swishing hiss.

Donny Hinson · Post by **Donny Hinson** » 5 Feb 2023 8:23 am

Of course the tubes are the first thing to check, as Dave said. But another thing that will cause tons of hiss is if the 820-ohm negative feedback resistor has a bad solder joint, or is open, somewhere. (A wire goes from this resistor on the board to the extension speaker jack.)