MkIII acting out - heard I was selling

[Zoner]

Crap, my MkIII blue stripe combo I was selling pulled a fast one on me today as I was doing another A/B to convince myself it was indeed expendable since the C+ came into the house. Jamming along when it started to hum - MMMMMMMM, pretty loud like someone grabbing a cord end plugged into the amp :shock: . I dropped the volume, looked around back, everything looked cool tube-wise (nothing glowing out of control), jiggle, jiggle on the output tubes, smacked it once or twice (take that you insolent POS! :evil: ), then switched it from class A to simul which cured it instantly. It happened again a half hour later and I had the same result flipping it at the mains off then back on again-cured. Any suggestions short of sending it off to Mike B.? I'm gonna pull the chassis and see what I can see. I also have a brand new set of 6l6's I bought for the C+ so I'll see if that helps, although I have not been able to recreate this situation again. I obviously don't want to sell it risking having it crap out on a new owner. Thanks in advance. Z

 

[Boogiebabies]

It could be a dirty standby switch. If the contacts are shorted there is no high voltage through the choke. Spray some contact cleaner in the switch and flip through it a few time. If it still acts up, remove the chassis and blast some contact cleaner into the switch on the terminal side. They actually have openings by the contacts.

 

[rippingrudy]

Bad Tube.

 

[Boogiebabies]

Bad Tube.

Yes, could be the V1.

The three major reasons for loss of output:


Dirty Stanby Contacts

Loop Jack Contacts

Angry V1