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What’s wrong with these McIntosh Monoblocks?

Evening, got a question about these two McIntosh MC40 amplifiers. I got them from garage type environment, humidity was present as they have some surface rust, but absolutely no damage or dents. Opened them up and did a visual inspection, nothing looks burnt out or bad. However, I replaced the fuses as they were both burnt out with ones that were identical, ensured the voltage setting was correct, plugged the amps in(no speakers connected), and nothing. Removed the fuses to find them both burnt out again. What could be causing this? Would be eternally grateful to anyone who can help.

polak
czarivey
5,946 posts
 

If fuses blow right-away, chances that you have bad output stage are dominant and you will need to inspect output stage components such as DC supply literally one by one if you don't have schematics certainly starting from output tubes. After testing one or few bad output tubes, don't be in the rush placing new tubes!!! Inspect components around tubes such as caps, resistors, large filter caps and resistors around large filter caps.  

jond's avatar
jond
5,807 posts
 

Take the amps to a tech who can work on them any of a number of things could be wrong. And as said above always use a variac and ramp up the voltage slowly. A sudden inrush of current can do damage to long unused electronics.

asvjerry's avatar
asvjerry
4,618 posts
 

As Clint said..."Are you feeling lucky?"

Good luck. 🤞👍

bigkidz
3,381 posts
 

@aball - correctamundo - I am in New Jersey if you need repair assistance.

 

Happy Listening.

elliottbnewcombjr
5,375 posts
 

problem now is the same as what blew the fuses in the 1st place. unusual that both amps fuses were blown, and both blew again.

fuse specs: perhaps someone put the wrong fuse in them. find the fuse specs, get a couple pairs of them, see what happens

how rusty, i.e. if they need work, fix spend money, could you re-sell them for a profit?

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