HIGH pitched squeal after about 10 minutes

[MRX2099]

I have another amp rig other that my plexi clone. My rack mount systems consisting of a (1)Mesa Recto Pre Preamp, (2)Mesa 2/100 Power amp, (3)t.c. electronics G-major, (4)482i sonic maximizer and lastly (5)a Furman M-8L power conditioner. I turn that system on normally then in a few minutes I switch the standby on the preamp then power amp to on, play, then about 8-10 minutes or so when it starts getting warmer there is a real high pitched squeal coming from somewhere. I though it was where the system is on the same room as my computer maybe the monitor was interfering, but when I switched off the monitor it still does it.

I unhooked the 482i and ran it without that, then pushed the BYPASS on the g-major to bypass it, but still get the squeal. I tried tapping the tubes with a pencil eraser to see if any certain tube was bad , but did not get anything different. I live in such a PODUNK town now, there is one small music store not so close by (about an hour away.) I took out all the tubes out and was going to get them checked today, but their tech guy ( whom does not even work for them just stops by often to see what they need checked of fixed, was not there and no-one else there could stick their finger up their........er......... I mean knew how to test the tubes........................

any ideal if it may be something else of could it be just one of the tubes, I purchased everything used , but the PREAMP was only about a few months old so I know those tubes should be still good.......

Thanks
Jeff in PODUNK USA

[MRX2099]

Hrmmmmmm I was putting the tubes back in and when I got to the Power Tubes, I see 2 disturbing things looks, like 2 of the tubes have the center black pieces broke off that go into the center of the tube socket (don't know if that happened when I was taking them out or they were like that already and that was causing the problem, or) ...... but then one other of the sockets itself has black burn marks around 3 of the pole pieces where the tube legs go in...... so either way I have to get 2 new tubes first and try that...

what would cause the black like burns on the tube socket itself??

Thanks
Jeff

[toner]

Sounds like a tube failed and arced between pins leaving a carbon trace. You'll need to replace that socket or it will just arc again.

You may be able to scrape the carbon off with a razor but check it carefully. There may be traces on both sides and you may not even be able to see them. If it's a PCB mounted socket, check the board and nearby components for burn marks or other damage.

[MRX2099]

Will do toner, thanks............

So I am looking at at least 2 new tubes and possibly a tube socket, I will take the cover off the power amp tomorrow and see how its mounted and what the inside looks like, hopefully its all good or at least easy to replace...


Jeff

[MRX2099]

OK today i took the cover off and its all looks fine inside everywhere even on the other side and between the tube socket board. I started inspecting the tubes all very carefully and , voila, the 2 with the center "Key" for orientation that were broke, actually were just the plastic "key" piece not the glass, so I super glued those 2 back on.. however I saw one tube that has a large crack all the way down the tube, so I am guessing that is the one that was in the place of the arched socket...and causing the squeal....( it probably leaked out the vacuum and was arching since it was the bad tube) so over all I am only out 1 tube, hopefully my local shop has Mesa tubes or they can order them.


Thanks everyone I'll keep you informed on how it goes



Jeff