McIntosh A129 Monoblock

[Kamakiri]

Well, thought I'd start this thread to chart kind of the history and progress of this amp that I've purchased. Pics to come.

The first thing I thought I'd better do is obtain a service manual, since it appears that the transformer casings were hit a couple times with a hammer or something, probably by an ex wife or something :tongue: . Called McIntosh, and the response from their man was... "wow, you must have something really rare there, because I've never heard of it and it's not listed in any of our books". He suggested that I contact Audio Classics, which was my next call.....

"That amp is ultra rare", the parts man said. After asking about a service manual, he thought for a moment, and said, "Hang on, I'm going to transfer you to (can't recall the name). You really should talk to him on this."

So I'm pretty excited about this! How rare need an amp be so that the manufacturer wouldn't have it in their catalogs?

So after I post the pics of this sorry beast, and maybe after I talk to the guy at Audio Classics, I'm going to have to determine how to go about restoration.....or hell, maybe they'll give me an MI-3 in trade :D

[Wardsweb]

You can also try: http://www.mcintoshaudio.com/

[Kamakiri]

Pic #1, just started polishing on the left.

[Kamakiri]

Note the blanking plugs :confused:

[Kamakiri]

Might clean up halfway decently......

[Kamakiri]

Sad, isn't it? :(

[Kamakiri]

Back shot of the nameplate

[Kamakiri]

Not sure if the old girl will ever play a tune again....as I found 5 completely charred resistors under the chassis (which is very clean), but to determine further possibility I have to get the covers off those transformers to see what they look like inside. But, I'm not going to do anything until I hear back from Audioclassics, or maybe try the place Wards recommended.

[opt80]

Blatant amp abuse!Some people have no regard for anything

Alan

[MikE]

Congrats on the pickup. I'll be interested in seeing the amp refurbished. Hopefully, it will be restored and make you smile. MikE

[ronflugelguy]

Looks like a variant on a MC-75??????????

[moondog]

That's very sad that someone would let something that nice get into that kind of shape. Hope you can bring her back to life.

Just out of curiosity... How much does she weigh?

mOOn

[CarlV]

You're certainly the first on your block to have one of those! There
is rubber or like insulation between the transformer and
the cover, I tried on mine once and the cover doesn't want to separate. Those dents should be on the head of the idiot(s) who
did that. Vented chassis cover!, never seen one of those. No 5U4's so it well could be a MC75 variant having SS rectification.
Should weigh @48lbs. like one of my 60's I would think. Nice find
anyway!
Carl

[Haoleb]

thats about as bad as the MC240 i was given a few months ago. anyone remember that? well after spending over 100 in parts for the thing and installing them. come to find out one of the output transformers was shot! ARGH! but i was able to come out even. no debt. here is a before and after pic of what i could do. the silver spray paint was kina cheesy but it was alot nicer than plain iron.

[Haoleb]

And after a little grinding and sanding and like that.

[Rob]

Tim,

I just cannot believe that you paid $150 for that piece of junque. :yikes:

I'm glad that it turned out to be historically significant, like a rusty, encrusted cannon off the Titanic or something. :)

Rob

[moondog]

Kam - Don't know if you seen it, but Audio Classics has an A 129 listed for sale. That's about all I've found on that model.

http://www.audioclassics.com/detail.php3?detail=A129&nav=brand

mOOn

[Kamakiri]

Yeah, I did see that.....the only reference on the internet to this amp that I saw.

This thing has got to weigh 60 pounds easy. Hopefully I'll get a phone call today and we'll know a bit more :)

[Kamakiri]

Lots of theories, but nobody knows exactly what it is :dunno:

I've called every Mc expert on the net that had a phone number, somebody said that it might be produced for the military, another fellow who was quite knowledgable and friendly told me that he guessed that it was commercial issue, for radio station or theater usage, from the late 1950s.

Time to start sending a bunch of emails out.....this is fun :)

[reyneman]

May not help, but then again...

The A-128 is also known as a KS-16622-L1, made for Western Electric (part of Mc industrial line)

Mayhaps a search on Western Electric would find a nugget.

Just a thought (and they don't come to me often;) )

[Wardsweb]

modified MC75 for Square D

info from: http://www.roger-russell.com/amplif2.htm

[Kamakiri]

Interesting guys! Where'd you come up with WE, Reyneman?

And what the devil is Square D?

[Rob]

Square D is a company that manufactures electrical circuit breaker boxes, panels and related electrical hardware for power distribution in homes and commercial buildings.

[Kamakiri]

I came up with the same thing on a Google search, but the question is why would they need to have custom built Mc gear? For what purpose?

[Rob]

Here is why. Ever connect your speakers directly to a breaker panel?

[Kamakiri]

You're missing my point.....why would they need custom manufactured amps? For what application?

[reyneman]

Kama- contractors usually bid on power, control, and audio cable installations as a package- much cheaper to the buyer that way.

Many contracts 'speced' the equipment to be used, making a 'one stop manufacturer' desireable (just spec all ??? equipment).

The OEM equipment would be of the same quality as the name versions, but anything to do with looks or name brand would be deleted to save $.

You know, how Acura uses Honda parts but charges more...:)

[McIntosh-Chuck]

Hi, guys,
That is one of the many Industrial models McIntosh made for various labs and such in the 50's 60's and a few in the 70's (you may have heard of the 2500's that the Navy used for sonar in subs). Later Industrials got the MI prefix, (McIntosh Industrial).
Many Industrials were not even made for audio but for lab testing so watch out, not all are of any use. Some just got different output connectors or Impedance taps and are useful. (Like the MI3500).
As for the A129, I dug around in Sidney Corderman's old notebooks and found a A-120, made for Bell labs in 1957, it is a modified MC30. The A129 is likley a later version of that, as other industrials got totally different model names. I will see if anything exists on the 129, but dont hold your breath.

Play 'em loud,

[Wardsweb]

Chuck - according to Roger Russell it was a modified MC75 made for Square D.

[McIntosh-Chuck]

R.R. would know if anybody would, I just got REALLY dusty looking for a scematic for you but no luck.
I found all kinds of cool stuff, though.

[grumpy]

Man what I wouldnt do to be able to go through those files :scratch2:

Oh yeah welcome aboard Chuck.

[Kamakiri]

The question remains though, what was the purpose of this amp? How was it used? How do you even plug it into a wall? :confused: (there doesn't seem to be any place for a line cord to exit)

Chuck, my first inclination is to drill out the rivets on the transformer cans to check for damage. Would this be an advisable first step?

[millerdog]

Sorry for lack of content in my post, but this is a really cool thread!
Let the mystery unravel........:)

[Rob]

Originally posted by Kamakiri
The question remains though, what was the purpose of this amp? How was it used?

Tim,

That amp is a *boat anchor*! :D

[THOR]

Tim I have been following this whole thread and just gotta ask, why did you pay so much for this thing when you didn't even know what it is or if it even worked?? Was it cuz it said "McIntosh"??? I mean it is a craptastic piece o' gear and all but WTF???? :confused: :confused: :confused: :confused:

[Kamakiri]

Originally posted by Rob
Tim,

That amp is a *boat anchor*! :D

Oh rob, let's not even go there when it comes to your ownership of useless things that far exceed the purchase price of this amp.....I'd double my post count ;) (so quit crapping on my thread)

To me Thor, the potential that this amp represents is worth more to me than what I paid. Hard to explain really, but something you just have to be in love with I guess.

[geespot]

Didn't Thor have a similar story about his CV's, I don't remember anybody raining on his parade.

It may turn out that this is the only one ever made. Finding the history is half the fun of this hobby.

g

[Rob]

Tim, All,

Maybe not commonly known in these circles but "Boat Anchor" is an affectionate term often used to describe vacuum tube equipment by their owners and related special interest groups.
The more 'iron' on a chassis, the more it qualifies. :)

No denigration was intended.

[Rob]

Geespot,

I'm not raining on Tim's parade at all. My comments were made in fun and were apparently misunderstood, by Tim too. Sorry Tim.

Thor,

I can understand why Tim would have bought this. Tim is in an "exploring Mc" phase right now. When you see a McIntosh label on a tube amp you know that you have found something many consider special, s'true. Add to this the fact that it is not one of the common pieces of Mc gear that we see and that probably added to the excitement of the 'score'.

[THOR]

Now, now, no raining just trying to understand the madness, if my CV's had been in the shape that amp is in (seriously looks like someone took a hammer to it) I never would have bought them no matter how rare, I also didn't know they were rare at the time I pretty much bought them cuz of how huge and beautiful they were ;) So I'm not trying to be rude or nothing I just wanna understand the WHY behind the purchase I am not meaning to offend.

[THOR]

Kind like how a lot of us asked about the old tv thing remember ;)

[McIntosh-Chuck]

You never know what you might get, I bought a weird looking McIntosh at a garage sale 20 years ago, I thought it was a piece of test equipment, dont know where it ended up, when I started working at McIntosh I realized it was a 10W-50!

I am off to CEDIA now, so anybody near Indy should come see the McIntosh booth , we have a 3,700 watt theater with 118 drivers!

as for opening the transformer, I am not a restorer, so I dont really know. Ron-C gave me a clue for where to find history on that a129, so I will look some more next week,

play 'em loud,

[Kamakiri]

Well, since the amp's not doing anyone any good in its present state, I decided to begin work. First thing I had to do is to get the transformer covers off and see what damage was done inside.

After drilling out the rivets holding the cover to the amp, I discovered that I didn't need to drill them out at all :mad: . The covers come off with the bolts from the bottom. Not a big deal though, as I can match the rivets up from the body shop at work.

I get the cover off, and the transformer is potted in about 5 pounds of black tarry goo :mad:

I tried applying some heat with a heat gun, and that got some of it, but it would have taken forever. So, brought it to work, and fired up the oxy-acetylene torch up on low heat and went over the outside case a few times. In about 15 seconds, the tar holding the transformer in place loosened up, and pop! Out came the transformer! :) . Getting the tar off after that was simple. I'm going to save it and reheat it to seal it up when I'm done.

My only problem is that, since it seemed far easier to snip, disconnect, number, and then reconnect wires than to desolder them and fish them around and out (I have a far beter chance of getting it right personally doing it that way, trust me on this one), I labelled all of the wires by number, and of course two of my number tags got burned up :mad:

So anyway, here's where I'm at......the cover is going to the autobody shop at work tomorrow.

[Rob]

Tim,

Good for you. I'm glad to see you tackling this project. :) Have fun.

Shouldn't be too hard to figure out what wires those are that lost the ID tags with an ohmmeter. What one was it?

[Kamakiri]

Actually I don't think it's going to be hard either, there seems to be enough color left in the fabric wires to match them up.

So the next question is, what would be the best way to test the transformer to see if it's any good? How do I go about it?

[Wardsweb]

First thing will be to ohm it out, DO NOT apply ac power to it yet. There will be two wires that are the input to the primary windings on the amp. This is where the 120vAC would go from the wall. Now there will be several secondary wires. These will ohm out to different ohms, as they supply different AC voltages to the amp. Without a schematic I can't tell you what the ohms are or what the voltages would be if power was applied, but you should get some ohm readings. It should not read open or no ohms.

[Rob]

Transformers can only go bad if they get shorts between turns or to the case, or if windings go open. It is extremely unlikely that they are bad unless the dents in the outer case mashed the winding stack. If the inerds look physically OK I'd assume they are good and proceed with restoring the amp. You could do an ohmeter check of the windings. This is when you need that service manual I steered you to on ebay with the schematic. It would likely have had the winding color codes identified. Mc used cathode feedback on their output xfmers so there is an extra winding or two to be found from conventional output transformers.

[Kamakiri]

Well, we've got the dents and holes in the one said transformer can all patched up and in primer. I'm going to wait until the transformer is tested and repotted back in the case with all of the original tarry stuff to apply a coat of paint.

I set the case still in primer on top of the chassis to show how much of a difference from A to B :)

[VinylHanger]

Wow those body shop guys did wonders with bondo :p:
Very nice :)

[Kamakiri]

All of the holes were spot welded and ground before the glass went on, just a skim coat as they hammered out the dents too :)

[Rob]

OK, I gotta question. I see your new signature line has misleading temperature information. How can it possibly be so many degrees C in Buffalo? That's like my Canadian weather channel reporting that "they had so many centimeters of snow fall in Buffalo". Can't happen. Buffalo news services know how much snow falls in Buffalo and they will tell you "so many inches of snow fell".

Same reason Canadians don't have to worry about Americans taking our water. Canadian water boils at 100 degrees. Your water boils at 212 degrees. You wouldn't be able to use our water because your coffee made from it would be too cold, your clothes wouldn't come clean in a hot water wash, etc.

Actually, modifying the American tempertaure (an American commodity in this case) reading to appear like a Canadian commodity is obviously something done for the purpose of exporting a service to Canada. That being the case aren't there issues like export and import duties and tarriffs to contend with by using your new signature? Is this even covered under NAFTA? :D

[Rob]

I'm somewhat disappointed. I thought my rant would have gotten a response from someone. Everybody sleeping out there or what? :D

If y'all were worried that I'd lost my sanity and were politely abstaining from commenting, don't worry I was just kidding. Everyone pretty much knows the Americans would love to get their hands on clean Canadian water, ...despite the fact that it now boils at a much lower temperature! ;)

[VinylHanger]

response :p:

[Kamakiri]

Well, I've decided now I may have a little time to invest in this amp once again, so I placed it back on the workbench.

Let's get some input from you guys. Removing the transofrmers is pretty necessary to get all of the dings and dents out of the cases, so even if they're okay, the effort is well worth it. But after examining the amp in detail, I'm thinking, what went wrong here???

So what I've done is take a few pics and I'm going to give a little explanation to what I see, and see if anyone here can make a perspective call. Now mind you I have no idea where a cord for this amp might even be attached, or if it runs off 120 VAC at all, since I don't know what this amp is. But, it looks like everything that did happen to lead to its demise happened all at once and for one reason only, at least that's my guess.

Here's the first pic, which is a burned unknown resistor. It goes from pin 4 of the one KT88 to the junction board, to what appears to be a wirewound resistor, to pin 3 of the next KT88.

[Kamakiri]

This resistor of unknown value goes from pin 6 of the 12BH7 to pin 6 of the 12AX7

[Kamakiri]

This is a 21 ohm resistor, 10% tolerance, from pin 4 of the 12AU7 to pin 3 of the 12BH7. You can also see a couple other burned resistors on the board in this shot.

[Kamakiri]

Shot of the amp's underside

[Kamakiri]

Shot of the amp's underside with the the cover in place. Note that it is a perforated cover, and why the cutout????

[Morden2004]

Kamahiri said: what appears to be a wirewound resistor, to pin 3 of the next KT88

Digging way back into my tube amp design and building days, I think those "wire-over' resistors are not wire wound resistors. I think they are chokes wound over carbon resistors and are used to supress transients - usually in the cathode or screen feeds. It's been a long time but do recall actually winding several of these by hand when I couldn't aford to purchase new components.

Anyone else recall this product?

Paul

PS: Nice project! Makes me a bit sad that I gave away my last home-built amp last year.

[Morden2004]

OK, you wanted input.

First, have you metered the transformer as per Wardsweb's suggestion? That is a required first step. Because determining transformer windings can be a bit hit-and-miss unless you have the lead colors from a schematic.

Next, it would be best if there was a schematic of this puppy. Any chance at all? If not available, can you draw one out from the physical amp? It would help a lot. I have some typical circuits around here somewhere and we can do some matching once we can see what's what.

Paul

[Haoleb]

well looks like youve got quite a job ahead of ya on this thing. All i can say is good luck, fixing old MCintosh stuff isint my forte lol but maybe you will have better luck fixing yours. I cant speak for the resistors which look pretty shot, that thing definetly went up in a puff of smoke. but i believe the part on the far side of the board which has the cutout in the cover, facing down on the monitor. yes that part is a selenium recitfier, which is toxic. I know you can replace these with a diode and resistor device because thats what we did on my MC240 when i was repairing it.

this site has some info on the MC240 and points out parts and stuff. might be intersting to look at anyway. MC240 (http://mysite.verizon.net/res78w95/index.html)

[Rich Andrews]

I have seen that site before and unless I am reading things wrong, some of the text resistor values are wrong. For example in the first picture at http://mysite.verizon.net/res78w95/id2.html

R16 he says is a 30k and according to the pic the colors are green-blue-orange or 56K. R22 is a 120k not 12k. There are many more errors, so beware.

Here is a cute javascript color code convertor:

http://webhome.idirect.com/~jadams/electronics/resist_calc.htm

[dewickt]

That is the strangest looking MC40 that I have ever seen, you are in for a real job figguring out the circuit, a MC40 has all its parts mounted on the terminal board like a 240 does.

[doodlebug]

I've spent the last few minutes reading all the posts on this amp-of-mystery. Here's my guess for what it may have been used for:

Most likely: It was made for Square D to drive a shake table/vibrating platform of some sort. The only argument I can see for this application is that the amps were usually higher in wattage than this one appears to be able to produce.

Second most likely: It provided a solid 60 Hz or other frequency (like 400Hz for aircraft) signal for testing breakers and other power control devices.

- This may account for the hole cutout on the bottom of the chassis, which may have been used for a way to control the power input in some way.

BTW, just the amount of contributed expertise to dig out detailed information on this amp (can we call it that?), is just amazing.

Thanks for drawing us all into one of the more rare Mc devices I've ever seen.

Cheers,

David

[Rich Andrews]

I have a MC2500 that was used in the Oil Exploration industry. It had an additional back panel on it with some Mil type connectors one of which was labelled "Tow Fish". That is only strange amp that I have seen. I did dig up some additional info about it but since I have a tendency to yack too much,I will shut up now unless someone wants all the gory details. (:>)

[Kamakiri]

Actually Rich, I'd love to hear about it! :)

[CarlV]

I sure would like to hear about it!

Carl

[Kamakiri]

I decided after dead end to dead end, to call Square D.

Ended up speaking to a really nice guy over there who's been with the company quite a long time. Apparently Square D at one time produced a system called the Square D Elan, which was a residential in-home full control system for music reproduction with speakers placed throughout the home and a single control panel to control the speakers. In 1995, that part of the business was sold and is now http://www.elanhomesystems.com/ . According to the gentleman I spoke with, he had no recollection of McIntosh ever having contracted with them, that their systems were amplified mostly with Jensen components. He was kind enough to give me a phone number to contact Elan directly.

Next phone call.....

Ended up in touch with another really nice fella, Mr. Ross, over at Elan. He'd never heard of McIntosh being used in one of their systems either, so he went and spoke to the VP of their engineering department. He couldn't recall McIntosh gear being a part of their systems either, so he kindly offered to look into it for me if I would send him some pics.

The most ironic thing, is that when Mr. Ross put me on hold, what was playing on hold but Boddhastiva!

Karma I tell ya! Karma! :D

[Rob]

Originally posted by Kamakiri


.....
The most ironic thing, is that when Mr. Ross put me on hold, what was playing on hold but Boddhastiva!

Karma I tell ya! Karma! :D

And would a Boddhastiva be animal, vegetable or mineral and be larger or smaller than a breadbox? :dunno:

[Wardsweb]

OH Pleeeaaaaasssssssee :saywhat:

Steely Dan - BABY - Steely Dan

[Rob]

Originally posted by Wardsweb
OH Pleeeaaaaasssssssee :saywhat:

Steely Dan - BABY - Steely Dan

Sorry 'bout that. My eyesight has gotten so bad I can no longer read the tiny writing on CD cases so I don't worry about the names of any songs at all. I just know 'em to listen to if I like 'em. ;) My identification resolution goes about as macro as the name of the album these daze.

[ron-c]

Kamakiri,

What you have is an MC75 that has a custom output transformer that appears to only have one tap of some unknown impedance.
Rather than use an RCA input they are using some of the speaker terminals for the input. This was common on industial units and the MI200 is like this. This is also your tip off that the 2,4,and 8 ohm impedances are not available.
The inside looks like a MC75 that had a plumber work on it! The outputs should have the wire wound inductors and 2, 220ohm sand block resistors run between them. McIntosh would not use the 5 watt resistors running between the small tube sockets. On the end of the board by the output tubes there should be 2, 12 uf electrolytics for the bias but they seem to be MIA. Yikes.
If you pick up an MC75 schematic you should be able to compare.
The hole in the bottom screen looks to be for access to the fuse which by the looks of the inside blew often.

Ron-C

[dewickt]

Ron-C, look at the length of the terminal board, does it look short to you ? I think I had better get a MC75 and take some pictures of the bottom and post them.

[Rich Andrews]

K,

Do you have part numbers for any of the transformers?

[ron-c]

The terminal board is the right length for the MC75 but the stereo units like the 240 and 275 are much longer. Those five watt resistors should be mounted on the board behind the 12bh7. The amp if very far from original inside.

Ron-C

[Kamakiri]

Part number for the one transformer is 043-343, the other is the one I had redone, and I put the tag in a special place....now I just have to find it :confused:

[Kamakiri]

Email from Elan:

Tim

What a very interesting device! The pictures also helped me determine that this is definitely not an ELAN or SquareD/ELAN product. I’m a little baffled why McIntosh was unable to help you as it clearly has their logo on it. I’m trying to imagine what the Square D number relates to, but this unit definitely predates the existence of ELAN as an individual entity or as a subsidy of Square D. I had hoped that we could shed more light on this, but this unit is not related to us in any way... Good luck w/ your project!

Brent Ross

ELAN Technical Writer/Support

[Rich Andrews]

K,

If you call McIntosh with the part numbers to those transformers, they might be able to tell you something about the equpment they went into. Call it reverse engineering. (">)

r

[Kamakiri]

That may be the next step. I'm beginning to think, however, that this piece of gear was created for Area 51 :tongue:

[opt80]

Originally posted by Kamakiri
That may be the next step. I'm beginning to think, however, that this piece of gear was created for Area 51 :tongue:

Maybe it was brought here from"away":zoom: :yikes:

Alan

[CarlV]

Hey Kam, You were able to safely remove the decal? Care to share tips? I would appreciate it.

Carl

[Kamakiri]

These weren't exactly decals, more like thin metal plates. Slid a razor blade under it and it came right off.

[CarlV]

Interesting, the ones on mine look like decals. I've thought about
a re-paint of my 45 year old 60's. If I do I won't sweat about removing them I guess. They really don't matter that much to me and I will be buried with them. ;)

Carl

[Rich Andrews]

Carl,

Depening on what they look like, maybe a touch up with a brush and then a coat of clear flat or satin would be all they need. You might be surprised what a coat of clear will do. Be careful because some new spray finishes will dissolve the old paint.

[CarlV]

That would be worth a try before I go to the extreme trouble
of stripping and painting. Fortunately there are no dents, just a few nicks in the paint. Time's on my side, and they aren't going
anywhere. :)

Carl

[Rich Andrews]

If there are just a couple of small scratches, try a Sanford Sharpie. You would be amazed at how well that works on black anodized aluminum and other black painted pieces.

[CarlV]

I've tried that before and it doesn't work on the transformers.
It does work great on heat sinks and some other stuff.

Carl

[Rich Andrews]

Thanks for the tip Carl. Sorry to hear it doesn't work. (:<)

r

[dewickt]

Here are two pictures of a virgin MC75.

[dewickt]

And here is the back side.

[Rob]

I see it has those capacitors that were labelled like resistors because that is what they turn into as they age. That aside I think these pics will be helpful to Tim in his restoration, especially if he cannot find another schematic. Those resistors (the real resistors not the capacitor resistors) are easily identified in the pictures.

[dewickt]

Here is a shot of the output sockets.

[dewickt]

Slightly out of focus but here is a bottom shot, only had the camera for 5 years and still keep forgetting how to get a good closeup. As an after thought, the amp in the pictures has Gold Lion Genelex outputs and problems, will fix it tomorrow night.