• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

McIntosh MC275 problem.

Hi all,
Recently I bought a McIntosh MC275 valve amp.
My first question to the seller was "is it 120 volts or 240. (Australia has 240)
He assured me it was 240 volts. A week later I bought it.
It came with an Australian power cord (fits straight into our power points). (He could have just thrown that in easy enough)

On the chassis above the power input it states 110~120 volts. The print on the PT says the same. Also has a 4 amp fuse which suits USA voltage. (Aust 240v requires a 2 amp fuse).
I have a stepdown transformer which I used but valves barely light up with next to no heat and sound is quite distorted with no power.

Could it be that it really is 240 volts. Not wanting to fry it I'm not going to try it, but it does seem like it's only getting half the required voltage :confused:

So, at this stage it is in limbo. :(

I am not so knowledgeable about PT's but according to diagram on top of PT there seems to be 2 primary coils. (correct me if I'm wrong)
I don't know how they are connected. Not willing to open it up yet. It's heavy too - 67lbs.


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When the diagram is correct you should connect GRY/BLK with VIO/WHT.
Then the Black and White taps should give some 234 VAC.
Also try to check the negative supply for the power tube grids.
We have an MC275 (maybe older type) which had a prehistoric rectifier; negative grid voltage was quite a bit lower than the specified -57 volt so the power tubes draw too much current.