Pleas help identify this McIntosh valve amplifier

Rodeodave · 15th March 2010, 01:33 AM

In short, I got this from a friend. It looks like commercial product that uses two massive (OEM?) McIntosh amplifiers. It's really heavy

The tubes are 12AU7, 12AX7, 12BH7, 12AT7 and two KT88. The input is BNC and the print next to the potentiometer (with switch) reads "2.0V setting for McIntosh preamp. There is a speaker output-strip with labels "GND,COM,4,8,16". There is also an output-socket that seems to be feeding some higher-impedance loads.

I can make more pics tomorrow. Can anyone identify this beast?
Could the amplifiers be operated @ 240VAC 50Hz with a sufficiently large step-down transformer or would the 50Hz cause trouble (less efficiency)?

Glowbug · 15th March 2010, 01:43 AM

Looks like some kind of lab-grade signal generator...maybe you could remove the frequency-determining part of it and run them full range

munorc · 15th March 2010, 01:53 AM

Looks like a pair of MC 75 monoblocks.

HollowState · 15th March 2010, 01:54 AM

You lucky dog!! They are in fact McIntosh MC75s The output and power transformer numbers clinch it. I'm sure because they are the same as mine.

Glowbug · 15th March 2010, 01:57 AM

Rodeo, do you have a better photo of the faceplate?

munorc · 15th March 2010, 02:00 AM

I do not think it was uncommon for them to be used for non-audio applications. The one I showed above was from a collection we had in a University engineering department. They were used, in our case, as small shaker amplifiers for vibrations testing.

(An MC 40, 60, 75 and 275, not in the order pictured)

Rodeodave · 15th March 2010, 02:02 AM

Here you go.

Eli Duttman · 15th March 2010, 02:09 AM

I'll venture a guess and say that's some sort of instrumentation, with a pair of MC75 based amps in it. The MC75 schematic is here.

McIntosh did not skimp on "iron". I don't think you need worry about 50 Hz. mains. Buy a pair of Allied 6K175VCP or equivalent 2000 VA step down autoformers. "Mac" circuitry is Class "B" and you don't want adverse regulation effects in the autoformer. Thank Kevin K. for that tip.

The "iron" in your possession is GOLDEN. Do a full stem to stern refurb with modern parts. Then play those monoblocks regularly. You will be smiling.

That's quite a find and I'm jealous.

Rodeodave · 15th March 2010, 02:12 AM

This is from the estate of the late husband of a friend's kindergarten nanny who called him up to clear his garage after 40 years of hoarding...we spent the whole day there assessing the vast of his collection. Mind boggling. We'll be back in two week with a van. I remember a 1.5kVA step-down transformer that'd go nicely with the twins...

Rodeodave · 15th March 2010, 02:30 AM

Would you guys use WD-40 to clean the amp?

15th March 2010, 01:43 AM	#2
Glowbug diyAudio Member Join Date: Feb 2006 Location: Hillsborough, NC/McLean, VA	Looks like some kind of lab-grade signal generator...maybe you could remove the frequency-determining part of it and run them full range __________________ Jim J.

15th March 2010, 01:54 AM	#4
HollowState diyAudio Member Join Date: Aug 2006 Location: Taxland, New Jersey	You lucky dog!! They are in fact McIntosh MC75s The output and power transformer numbers clinch it. I'm sure because they are the same as mine. __________________ "The supercomputer is technologically impossible. It would take all of the water that flows over Niagara Falls to cool the heat generated by the number of vacuum tubes required." ~ Professor of Electrical Engineering, New York University

15th March 2010, 01:57 AM	#5
Glowbug diyAudio Member Join Date: Feb 2006 Location: Hillsborough, NC/McLean, VA	Rodeo, do you have a better photo of the faceplate? __________________ Jim J.

15th March 2010, 02:09 AM	#8
Eli Duttman diyAudio Member Join Date: Apr 2004 Location: Plainsboro, NJ	I'll venture a guess and say that's some sort of instrumentation, with a pair of MC75 based amps in it. The MC75 schematic is here. McIntosh did not skimp on "iron". I don't think you need worry about 50 Hz. mains. Buy a pair of Allied 6K175VCP or equivalent 2000 VA step down autoformers. "Mac" circuitry is Class "B" and you don't want adverse regulation effects in the autoformer. Thank Kevin K. for that tip. The "iron" in your possession is GOLDEN. Do a full stem to stern refurb with modern parts. Then play those monoblocks regularly. You will be smiling. That's quite a find and I'm jealous. __________________ Eli D.

15th March 2010, 02:12 AM	#9
Rodeodave diyAudio Member Join Date: Dec 2004 Location: in the alps Blog Entries: 1	This is from the estate of the late husband of a friend's kindergarten nanny who called him up to clear his garage after 40 years of hoarding...we spent the whole day there assessing the vast of his collection. Mind boggling. We'll be back in two week with a van. I remember a 1.5kVA step-down transformer that'd go nicely with the twins... __________________ Gravity - Making the G since 13.7 billion B.C.

15th March 2010, 01:53 AM	#3
munorc diyAudio Member Join Date: Mar 2009 Location: Minnesota	Looks like a pair of MC 75 monoblocks.

15th March 2010, 02:00 AM	#6
munorc diyAudio Member Join Date: Mar 2009 Location: Minnesota	I do not think it was uncommon for them to be used for non-audio applications. The one I showed above was from a collection we had in a University engineering department. They were used, in our case, as small shaker amplifiers for vibrations testing. (An MC 40, 60, 75 and 275, not in the order pictured)

15th March 2010, 02:30 AM	#10
Rodeodave diyAudio Member Join Date: Dec 2004 Location: in the alps Blog Entries: 1	Would you guys use WD-40 to clean the amp? __________________ Gravity - Making the G since 13.7 billion B.C.

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