Marshall 2550 SJ Humming and Whistling

[67Mopar]

Okay, so my 2550 started in with a nasty 60Hz hum this afternoon. I had been meaning to replace the 30 year old filter caps with new ARS caps, which I did do. I have new caps installed, but it still suffers from the same issues. When I plug/unplug the guitar cord, I get a whistling sound at the halfway point. I've never experienced this before with any amp. Doesn't matter if the other end is plugged into the guitar, or not... I still get the whistling sound. I tried three different cords, but the issue continue. Has anyone else experience this? Any ideas what is going on? I cleaned the input with Deoxit, and also changed the preamp tubes... Neither efforts helped.

[xtian]

Broken/intermittent connection? Prod around with chopstick.

[67Mopar]

Broken/intermittent connection? Prod around with chopstick.

Thank you for your reply, and that's exactly what I did. I replaced the replacement V1 tube with another tube after testing the socket connections.... Fixed! The filter caps original caps needed replacing, so it wasn't a complete waste of time. What are the chances of having two failed 12AX7 tubes? 1 in 3, apparently.

[Stevem]

With amps expect anything and try to be ready for it!

[Roe]

often the pots go bad on these amps

[67Mopar]

It was a crapped-out 12AX7.