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MC60 Hum!!

M

Mofifool

New Member
Wondering if anyone can help, I am no electronics tech by any means so here goes...
One of my MC60 amps suddenly started a loud hum through the speakers within seconds of powering on.
I thought it might be the MX110 but found it was an amp. I know which one but not sure what to do now.
Any suggestions for tracing the problem that I can do myself?

Thanks
Here is a pic i took there is what appears to be a burn mark on the board but nothing else looks burned?
 

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Looks like you've got a rebuilt MC-60 where the old resistor had been mounted too close to the board. I'm not clear that's the root cause of your problem.

I'll assume that the same hum you're hearing also occurs with the input control on the amp turned all the way down, correct?

If so, then, observation is your next job:

- Look for red plates on the output tubes. They'll be a nice, cherry red color and the tube will be throwing off a lot of heat.

- Does the hum show up as soon as the tubes warm up? If not, how to it manifest itself?

- Have you reseated all the tubes? What happens if you gently rock the tubes side to side when its powered up?

- Does the amp hum with only speakers hooked up?

- Does the hum come from the speakers only or can you hear it from the transformers?

Cheers,

David
 
I'm having the same problem today with one of my MC60's. A large hum when powered on. It gets louder so I power it off pretty quickly.

Here's what I've done to debug the process.

Switched out tubes with the left channel MC60 that works fine. Problem still with the bad (right) MC60. Not a tube problem I believe.

With input line disconnected it does the same thing.

Opened up the bottom and checked things out. No burnt resistors and all "looks" good.

Switched power cord to a new circuit. Same problem

Both MC60's were gone through about 3 years ago and caps replaced. Both units have been work fine for 3 years.

Any thoughts?
 
Pull the 12AX7 and turn it on again. If it still hums you may have a failure somewhere in the power supply.

Sent from my SM-N900V using Tapatalk
 
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