Randall RG50TC tube combo. Reverb whistling/whining and sound drops when playing note

[raigdar]

Hello, this is my first post in here, and as i can see this looks like a good place to post my problem.

First of all its a tube amp with 2 power tubes (5881WXT) and 4 preamp tubes (12AT7). And has 1 high input (which i play in) and a low input channel.

Last week i was playing on my Randall amp, and it worked perfectly both the clean and overdrive channel.

So i turned it on yesterday and it was letting me down big time, i hear this squealing/whistling noise from the speaker. I instantly turned the volume down to 0 and i could still hear the noise, i then began to turn the controls and found out the Reverb Control is the one doing it. When its turned to 0 theres nothing and as soon i turn it, it starts the noise.

I tried to unplug the cable from the high input and it stopped, i then tried to put the cable back in slowly, it instantly starts to squeal again (Please note this squeal is not very loud, because i have turned the volume all the way down, but does gets higher if i turn volume up and the reverb control up.)

I was thinking it could be a tube, so i removed the first preamp tube on the left and turned the amp on again, and tried to put the cable in the high input again and there was nothing. So i think i found the reverb tube.. i then tried to replace it with a brand new 12at7 tube i have in spare and it started squealing when i insert the cable.

(when i tap the tubes with a pencil i cant hear any difference on the sound)


Now to my other problem with my amp (sigh)

I then thought oh well, i just turn the reverb down and just start playing, but it wasnt that easy. As soon i play a note on my guitar the volume on the amp instantly cuts off to nearly hearable and back again when the note have played for a little while (2-3 secs). I tried to do it a few times and it just keep doing it, dropping down when the note is played and comes back up when the note have been ringing for a while.

I turned it over to the overdrive channel and again, as soon i play a note of some kind it instantly drops down.


I really hope you guys have some suggestions to these problems.
Ive been thinking it could be the power tubes gone bad.

Hope to see some suggestions to the problems soon .

Thanks very much!

[Chuck H]

Slightly strange symptoms. Nothing that can be fixed by external plugs and tubes. It's going to take bench tools and an open chassis to diagnose it.

[soundguruman]

In these amps, the reverb springs break or the wires inside the reverb tank break.
More often it's a broken wire in the reverb tank.
You probably need to resolder the circuit boards and clean the controls too.
Check the all the chassis ground connections.
Working on these amps takes plenty of patience and time because of the way they are designed and built. They are more difficult to repair.