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McIntosh A-120 Tube Amplifier

dumortier-us

dumortier-us

Dumortier-US
Hello: I have a pair of McIntosh A-120 rack mount amplifiers that I have had for a number of years. I purchased the two seperately over a period of about four years. They are both in very good condition, one slightly better than the other and one has the original face plate. On and off I have been trying to get information on the amps. So far, it looks like they were built by McIntosh on a Bell Labs contract for 100 units. I understand they are modified MC-30, but they appear to be much more robust. They came with KT88s and I did not believe the MC-30 was capable of handling this tube. If anyone is interested in photos, I would be pleased to provide some. I would be very interested in any information anyone can shed on these amplifiers. Over the next few weeks, I will be giving the a thorough checkoput prior to listening to them on my RCA LS-9A'a. You input would be greatly appreciated.
 
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Do post pictures of them here.

I wonder if they are A-116's with different output tubes?

mac116.jpg
 
No, they don't look like the A-114, other than the hammertone color. These are rack mounted, about two times bigger and three times heavier than the A-114. Hoe do I insert a photo into my reply?
 
Those amps would have been built by the Instrument division of McIntosh labs. All of that division's amps had a MI-xxx model designation. They were used for all sorts of PA systems, phone line repeaters, shake tables, etc.

I note one of the KT88s is gone from the white top. Judging from the tube compliment, I'd suggest that the circuit topology isn't going to be close to the MC30 - far more tubes for a mono chassis.

I'd suggest you post over in the McIntosh forum here at AK and also contact Audio Classics in Vestal, NY for more details. The transformer codes are important to determine the bandwidth of the amp, too. That's the M174, M175 and M176. The M174 appears to be the input transformer with impedance switching. I'd guess the M176 is the power transformer and the M175 to be the output transformer.

Nice set!

Cheers,

David
 
Yep, nice stuff! :) But that one tube has lost it's vacum as David mentioned.
Not at all like the 30's or 60's I have. It will be fun to hear the story on them. I am uploading your pics to the site. Here is a tutorial I made for uploading.
bolly still can't figure it out after all these years. :p:
http://www.audiokarma.org/forums/showthread.php?t=173832

Carl
 
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I am betting that is a Triad HS-1 input trans. Mc used them on a few 50's industrial units. Interesting piece. Would love to see the schematic for it.
 
A-120

Yes, it would be nice to have a schematic and more information on the amps. If the weren't so heavy I would take one out of the rack and try to do a circuit analysis and schematic. If I do get around to doing it, I will send you a copy.

Joe in Virginia
 
I am speculating that the circuit topography is like an MC-60 amp with an added preamp onboard. I doubt it is radically different from the MC-60 + a Macintosh Mono preamp. The MC-60 is 60wpc using KT-88 or 6550 type tubes.
 
McIntosh A-120

Hi Mike in MI:

I have had these for a number of years. They were, and are in the rack by my RCA LC-9A's. I found one about 12 years ago and found the other about four years later. Other than the two and one I heard was in Russia I've never seen another, nor have I found much info. I am hoping someone else can shed some light on the amplifiers and their history.

Joe
 
Hi Phototone:

Yes, I am sure the layout is similar to the Mac60 though it look more like a Grommes 260 with Mac transformers and a more elaborate attenuator. It does not have a true integrated preamp, only an effective gain control. It is a very pleasant amplifier to listen to and it does sound similar to the Grommes, more so than the Mac60.

Joe in Virginia
 
hi joe,
just a thought... maybe e-mail or send a pm to terry dewick. i am pretty sure if he don't know, or knows anyone that does... then well you know
david
 
Hi David:

I do not have Terry's e-mail address. If you can, please forward it to me, or ask Terry if its okay?
Joe in Virginia
 
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