MC 75 Blew a Fuse

[John Jordan]

Last night while listening to some sounds, there was a thud and then the music level dropped to almost nil. Cutting to the chase, one of the mono blocks blew a fuse.

I have read this can be power tubes or a rectifier tube. Not sure about this rectifier thing or if it even has a dedicated rectifier tube. I'll contact Mike at Audio Classics on Monday. In the mean time, the lone 275 has quite nicely stepped up to the plate. Any thoughts are certainly appreciated.

John

[FreddieFerric]

Originally Posted by John Jordan

Last night while listening to some sounds, there was a thud and then the music level dropped to almost nil. Cutting to the chase, one of the mono blocks blew a fuse.

I have read this can be power tubes or a rectifier tube. Not sure about this rectifier thing or if it even has a dedicated rectifier tube. I'll contact Mike at Audio Classics on Monday. In the mean time, the lone 275 has quite nicely stepped up to the plate. Any thoughts are certainly appreciated.

John

Really sorry to hear that John. Are you connections good, tight and solid? Not sure if the MC75 has the Sentry Monitor circuit, but in my 1502 the manual says the Sentry Monitor will activate upon instances of an imbalance in impedence at the speaker taps or when a tube is failing.

Absent evidence of a stray voltage surge I'd start testing the tubes if you can. For the internal fuse to blow you have to wonder if there's a short in there somewhere. (Hoping that's not the case).

[Formerly YB-2]

MC⁷5 has no rectifier tube.
Swap in a spare set of tubes and give it a try.

[FreddieFerric]

Originally Posted by Formerly YB-2

MC⁷5 has no rectifier tube.
Swap in a spare set of tubes and give it a try.

Originally Posted by Formerly YB-2

MC⁷5 has no rectifier tube.
Swap in a spare set of tubes and give it a try.

Good advice Glenn.

FWIW, the server has been super, super slow of late making posting a bit weird.

[John Jordan]

Fred and Glenn-

Thanks for the reply's.

Fred, yes the MC 75 does have the Sentry Monitor. I didn't notice the flashing stand by light but was not looking for it either. Initially I thought it was the 275 as the green lights went out but that appears due to lack for signal from the 75. I can pretty much rule out an impedance mis-match as this set up has been functioning for a while. I did check the speaker wires and power cables and continuity is in tact. So, I'll rule out a short and keep the finger crossed it's not an internal short.

Glenn, I do not have a spare set of tubes but I guess I could swap some out of the 275.

The sound with the single 275 is real good as with just the 75's; cleaner with bi-amping adding some fullness. After the 75's are back in order going to re-think this bi-amping stuff.

John

[Formerly YB-2]

Originally Posted by FreddieFerric

FWIW, the server has been super, super slow of late making posting a bit weird.

Was posting from my phone without my glasses, so was all me.

John - Good luck with your MC75. My favorite McIntosh amp(s).

[Stahle]

Originally Posted by John Jordan

Glenn, I do not have a spare set of tubes but I guess I could swap some out of the 275.

That's the first thing I would have tried only because I wouldn't want to swap out the amps, they're heavy! Give it a try and let us know if it fixed the issue.

[FreddieFerric]

Originally Posted by Formerly YB-2

Was posting from my phone without my glasses, so was all me.

John - Good luck with your MC75. My favorite McIntosh amp(s).

Vintage eyeballs. I got them too.

[John Jordan]

OK, i removed the power tubes that appeared a bit burnt, installed a good fuse and powered up. The fuse popped. It's off to be benched along with the other for good measure.

Stahle, yes these tube amps are surprising "heavy." The distribution of the weight with the transformers on one side tubes on the other is quite awkward. A few years back, I carried a 352 power amp to my car to trade for the 275. Despite the 275 being much lighter on the scale, it was almost as equally challenging to carry. Freddy, that 1502 must have been a real bear!

John

[FreddieFerric]

Originally Posted by John Jordan

OK, i removed the power tubes that appeared a bit burnt, installed a good fuse and powered up. The fuse popped. It's off to be benched along with the other for good measure.

Stahle, yes these tube amps are surprising "heavy." The distribution of the weight with the transformers on one side tubes on the other is quite awkward. A few years back, I carried a 352 power amp to my car to trade for the 275. Despite the 275 being much lighter on the scale, it was almost as equally challenging to carry. Freddy, that 1502 must have been a real bear!

John

A bona fide Grizzly. Did you see my video about that very topic?