MESA 2:50 troubleshooting

[Steven Latch]

Hi,

My 2:50 has been behaving strangely recently.

A few minutes after I power it up, the guitar sound is replaced by a loud buzz/hum that persists even when the volume of both channels is down to zero. I have tried powering off the last piece of gear before the power amp, a G-Major multi effect but no change.

It doesn't sound like old tubes passing out. When I turn on the rack, the sound is good. None of that thin sound that is typical of worn out tubes.

Anybody has an idea?

Thanks

Steven

 

[RJ2213]

their are probably also a few preamp tubes inside the chassis, have you checked those? i'm assuming both channels of the amp are having identical issues, correct? if so then it may be the preamp tubes that are essentially used by both channels. after the rig is warmed up does the problem persist until its been turned off for a long time, or does restarting it fix it for a period of time?

 

[Steven Latch]

Thanks: It turned out to be the 12AX7 as you guessed. Great sound up and running again.

 

[RJ2213]

excellent. as a techie i love having confirmation on my advice. in the past year or so have i been actually repairing tube amps, so it's good to hear i was right. I just did a full retube on my triaxis/2:90 after it started giving some volume swell issues, i'm convinced it was those same preamp tubes. either way, i shouldve retubed a long time ago, my whole rig came back to life again.