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McIntosh MC240 Missing Line Voltage Switch

Greg Arpino

Greg Arpino

New Member
A couple of years ago, my father passed on to me his McIntosh MC240 tube amp. Since then, I’ve paired it up with a C28 Pre, a Micro Seiki DD35 Turntable, and most recently, a pristine pair of 1981 Klipsch Heresy speakers. It sounds absolutely sublime, especially when listening to jazz.

The question I have relates to the MC240’s line voltage selector switch, or in my case, the lack thereof. It seems like almost every MC240 I see online has the line voltage switch. One of the only exceptions is the one pictured in the Ken Rockwell Review. I’ve done a lot of searching online and the only thing I could find was an old forum post saying that they were told it was a rare European version of the MC240. I am curious to know if anyone has any knowledge of why the line voltage selector switch is missing from my amp.

Thanks!
 
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I have a pair of 240s,and both have the voltage switch. This is NOT a 120V/240V switch. It is merely meant for adjusting to the level of the available line voltage,offering 117V or 125V settings. Think of it more as a high-low line switch
 
My original later 240 did not have the voltage switch, the MC240 I bought pre-owned did.
 
I see them mostly with the 117v/125v switch, but the late version was also built without, ... not sure why. Does it still have the M207A transformer? If so, it's dual-voltage, just the switch is eliminated.
 
Welcome on AK Greg Arpino

Many very old MCINTOSH amplifiers and other were made with a selector switch from 117 to 125V (AC V)
If you think that your MC240 is made to work under 240V you are wrong
nothing is missing in your amp
The only worldwide model produced by the factory are with a small rectangular red plate with the right voltage printed on it and with a black decal glued next to the voltage switch

C22 Worldwide model :

C22-worldwide.JPG

MA230 Worldwide model

MA230-worldwide.JPG

MC225 Worldwide

MC225-worldwide.JPG

MR71 Worldwide :

MR71-worldwide.JPG

and many other

Black decal closer to the voltage switch

Decal-worldwide.JPG

All models without this black decal and red plate switch ARE NOT worldwide models





.
 
Greg Arpino said:
A couple of years ago, my father passed on to me his McIntosh MC240 tube amp. Since then, I’ve paired it up with a C28 Pre, a Micro Seiki DD35 Turntable, and most recently, a pristine pair of 1981 Klipsch Heresy speakers. It sounds absolutely sublime, especially when listening to jazz.

The question I have relates to the MC240’s line voltage selector switch, or in my case, the lack thereof. It seems like almost every MC240 I see online has the line voltage switch. One of the only exceptions is the one pictured in the Ken Rockwell Review. I’ve done a lot of searching online and the only thing I could find was an old forum post saying that they were told it was a rare European version of the MC240. I am curious to know if anyone has any knowledge of why the line voltage selector switch is missing from my amp.

Thanks!
Click to expand...

Very late MC240 do not have the 117/125(?) voltage switch, the Laboratory having deemed it unnecessary apparently.

My MC240 is also one of the late models without the voltage switch.

DSC05572.JPG
 
The change was not just production date, I have a very late build that does have the switch, where I've seen older production date units without.

What is the number on the transformer?
 
SaturationPt said:
The change was not just production date, I have a very late build that does have the switch, where I've seen older production date units without.

What is the number on the transformer?
Click to expand...

Did the transformer numbers change?

I'd have to double check to be certain but I believe the serial number of mine begins 40GXX.

MC 240 (LATE) - Sold from September 1965 - April 1969. S/N: 10G01~58G76 (6,644 UNITS) (16,896 TOTAL MC 240 UNITS)

DSC05559.JPG
 
S/N 45G45 and higher have two primary windings in parallel in the PT, P/N: 043-655 and no switch. Before that S/N has PT P/N: 043-048 or M207A.

Maybe McIntosh intended the 043-655 to be wired in series for 220vac? Would be nice to know.
 
SaturationPt said:
S/N 45G45 and higher have two primary windings in parallel in the PT, P/N: 043-655 and no switch. Before that S/N has PT P/N: 043-048 or M207A.

Maybe McIntosh intended the 043-655 to be wired in series for 220vac? Would be nice to know.
Click to expand...
That would be the logical assumption, 220-250 VAC-50/60 CPS.
 
Thanks everyone for the quick responses. I am indeed referring to the 117v/125v switch.

It's good to know that are a few others out there who also don't have the switches on their MC240's. I also suspect that this has to do with old vs new with McIntosh phasing it out toward the end.

Given the sheer number of images of the MC240 floating around on the internet and the scarcity of those missing the switch, I have to assume that those produced without the switch must have been fairly limited.

Still, I would love to know why the switch was removed and whether or not it makes any difference in the performance of the amp.

2020-04-03_08-56-10_713s.jpg

Thanks again to all of those who responded
 
SaturationPt said:
S/N 45G45 and higher have two primary windings in parallel in the PT, P/N: 043-655 and no switch. Before that S/N has PT P/N: 043-048 or M207A.

Maybe McIntosh intended the 043-655 to be wired in series for 220vac? Would be nice to know.
Click to expand...

That could well be. Terry @dewickt once mentioned to me that he thought it was an export model...
 
Is the switch necessary? 117V is the most common, or the mean voltage really, throughout the US. As this is rated 117V without the switch I would presume that it is the same as the multi-volt with the switch on 117V and that it is much less likely in 21st century USA that you'll see line voltage above 120VAC, thus the 125V position is not necessary.

OTOH, if that were replaced with the ability to run 117/234 (aka: 220 or 240), perhaps that was seen as a higher value to McIntosh.

Based on the S/N of the change I would estimate the change was around late '68 or early '69 (the last production year).
 
The AC line voltage these days tends to be above 120v(varies) more often than not, so I have rewired all my 50 + yr. old McIntosh tube amps that provide the internal 125v tap, to put the tubes filament voltage in a more comfortable range, along with the HT/bias voltages.
When these 50 + yr. old tube amps were designed, 110~117 volt AC mains, were more common.

After doing so the amps ran cooler, as well, while meeting all their specs.

Just my experience.
 
Greg
My MC 240 sn 55Gxx does not have the voltage switch. There is a previous post here where a member explains Mac’s reasoning for the change. I was told by Audio Classics that PT #043-655 is the export version.
 
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