RM20 noise weirdness

[imagimotion]

I just picked up an RM20 combo from a fellow forum member (thanks, Jace!), and I had a really strange issue when I fired it up for the first time. I was playing around with a SL+ module for about 15 minutes or so, and everything worked great. I then swapped it out and put in an XTC module and was loving life for the first 5 minutes of playing until the amp suddenly popped and then cut out. It came back, but the sound was really low and fuzzy, and then it just had this super loud hum and buzzing with just a little bit of guitar signal. I made a clip of it that you guys can check out here http://imagimotion.com/RM20/RM20_bad.mp3

Last night I took out the power tubes and inspected them thinking one of them might have died, but they looked fine. I did the same with the preamp tubes, and all looked good. I then reseated all the tubes and powered it back on. I had the XTC module installed with the preamp gain cranked and the level output low, and I was able to jam on it for close to an hour with no problems. This morning I fired it up again with the XTC module and ran the output level close to max with the preamp gain around 11:00, and I jammed on it fine for about 45 minutes.

This is the first experience I've had with these amps, so I have a couple of questions I'm hoping someone can shed some light on. I noticed that the power transformer has a sticker on it that says it has built in thermal protection. Is it possible the amp was overheating, and the transformer was shutting down to protect itself when I had the weird noise problem? Is it possible one of the power tubes was a little loose from the shipping, and the problem manifested after a while of playing when presumably some mechanical vibration knocked it loose enough to cause a bad contact on one of the pins? I checked that the modules were properly seated each time I installed them into the amp, so I don't think there was an issue with the module per se.

If anyone has some insight as to what may have caused this, I'd love to hear it. It seems OK for now, but I'm a little worried that it could happen again.

 

[Mattfig]

Hate to say it but it sounds like a bad cable somewhere...I know that's an elementary piece of advice but it's one I wished I'd followed more closely in the past before I began disassembling **** in hopes of finding cold solder joints and such...Also get some Deoxit and clean the inputs...I know, simple...But probably solves more than half of the problems I've read and posted about...

Good luck!

 

[imagimotion]

I don't think it was a cable issue because that same cable has been working fine before and after. It does seem like there was a bad connection somewhere, but not sure what it was. After I took out the power and preamp tubes and reseated them, the problem has not returned. Knock on wood! I'm hoping it was just a loose tube.