Mod 50 issues

  • Thread starter Thread starter IHateRap
  • Start date Start date
IHateRap

IHateRap

Well-known member
The problem started a few months back. When playing the output would fluctuate. Full volume......1/2 volume....slowly come back to full....slowly drop down to barely audible. Once in a while I'd get a loud static-y buzz after the amp was off. Suspecting a tube issue I replaced all the tubes. Power tubes are now a matched pair of 5881s biased to 33mv. After roughly 2 hours of use the problem returned. I checked the bias... one power tube read 70mv the other 32.5. Could something be causing premature power tube failure or am I just having really bad luck?

Thanks
 
Interesting as I've been having the same problem with mine. Mine is now barely audible. I'll check the bias later today.

Checked bias and mine was right the acceptable range, but still getting no sound regardless of what module I try. Wondering if this is a 12AX7 issue. How do you check? Take the tube cover off and see if they "glow"?

Pulled tube covers off. V1 glows. The AT7 in the loop buffer and the AX7 in the phase inverter position do not glow.
 
ned911":3ffbqb2n said:
Interesting as I've been having the same problem with mine. Mine is now barely audible. I'll check the bias later today.

Checked bias and mine was right the acceptable range, but still getting no sound regardless of what module I try. Wondering if this is a 12AX7 issue. How do you check? Take the tube cover off and see if they "glow"?

Pulled tube covers off. V1 glows. The AT7 in the loop buffer and the AX7 in the phase inverter position do not glow.
Click to expand...

Update

I reseated the power tubes and set the bias. I was able to play for a little while before the symptoms started up again. I quickly turned all the controls down and checked the bias....it was still good. A short while later I received a PM from another forum member (marl3y) who suggested I clean the loop jacks with contact cleaner. I went ahead and did that along with all the other jacks. I think it did the trick....just played for about an hour and everything was fine. Not sure what was up with the initial high millivolt reading. Maybe it was just an anomaly. :confused: I'll keep checking it periodically just in case.
 
I inserted a jumper cable in the serial loop and everything is working perfectly. Will get some contact cleaner and clean the loop jacks as well.
 
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