F-50 powering off

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mwrenne

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I have had this problem a few times, when playing a gig or full volume band practice.

on channel 2, with contour. Master Volume 3/4 all the way up.

when the gain, goes past 12:00 the amp turns off. You have to unplug the power, unplug speaker cables and then it works for a minute or two then turns off again. This happens after playing for longer than an hour. The issue resolves itself if the gain is reduced.

-at first I thought it was a faulty speaker cable, I had been using a cable with cheap connectors that had after a show been smashed together in transport, and shorted out. Replaced the speaker cable and finished the next gig, and few band practices.

-looked like the old power tubes had finally died, one was glowing bright blue. Replaced the tubes with mesa tubes, band practice went well a few times. Then the same old problem.

-figured maybe there was a bad pre-amp tube. I had never replaced the tubes, and I bought the amp used so I figured it was not a bad idea to replace. worse case I had an extra set of tubes, which is something handy to have around anyways.

-I quit my band, and the amp has been only used at my apartment at low volumes, but pre-gain all the way up, no problems. Last weekend we used my gear for a backline, since the mesa was so versatile we used that as the main head for all the bands. It worked great for the first two bands, the third band wanted a lot more distortion, and again at a loud volume with the gain up past 12:00 the amp powered down, no lights nothing reduced the gain to 12:00 powered it back on, and it worked fine for another 4 hours.

any ideas? has anyone else had this issue?
 
You say "no lights - nothing." There's nothing in the amp that would make it do that, so, I suspect either a bad power switch or some intermittent connections near the power supply. If you giggle the power switch, does it make the amp go off and on - does it seem loose/not firm? Make sure the IEC power connector and footswitch are seated properly.

good luck. - Pat
 
Could it be heat building up? Maybe putting a fan on it could reveal if that is an issue? I only think heat as you imply the time and environment is consistent with the event. High volume levels over an extended period of time. I know mine gets pretty warm and makes my room noticeably warmer when played even for 30 minutes. Heat can warm up solder cause bad connections. Maybe if you play it with headphones at that vol without the speaker hooked up you could see if the reduced draw from the speaker changes anything. Just spit balling here, let me know how it turns out.
 

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