[morzh]

Some 8 years ago or so, I bought a vintage C22 McIntosh preamp. The ad said "professionally serviced."
I'd prefer to service it myself, but that was what was available, and then, OK, one job less. After all, I did not specialize in Macs. 

I did call the shop (they gave name in the ad) at some point, to ask some questions. They indeed existed.

So. I do not use it a lot, just occasionally. Recently I was listening to it, after having bought some new CDs, and the Tape Monitor switch dropped one channel. I wiggled it, it worked, and I decided it was time to use some Deoxit, for which today I opened the amp.

When I bought it, they did show some pictures that showed new caps (one being CE Manufacturing).
But today I saw some caps, the pics of which I have attached, that I do not think are new replacements.


So, I did spray some D5 inside the rocker switches, and am planning to replace the rest of the electrolytics.

   
   
   
   

[radiorich]

Hello Mike,
I agree with you some of those caps look old !
Sincerely Richard

[Arran]

Mike;
Those bluish-purple caps with the red lettering are old, the light blue can may be a NOS one, the brown United Chemicon one may be newer, I think there is a way to decode the marking to tell the model, and year if unknown. Not sure of the twist lock can, given that it has carbon comp resistors on the bottom tell me that it likely is either original, or an old replacement.
Regards
Arran

[MrFixr55]

I'd be a little more worried about some of those solder joints, especially those with so much flux.

I'm supposing that all those caps from "Audio Classics" are new. regarding the age of the "can", I don't know if carbon comp resistors are still sold; they are not found in new electronics, and I assume that the metal film jobs are superior. I also don't know if the caps on phenolic boards were a McIntosh design or are replacements for the older style "cans". Ther does seem to be one older cap on the terminal board above all those coupling caps.

I always hope that these newer electrolytics are designed to last much longer than the caps of yore, as my 2 largest audio mixer "boards" contain a ton of electrolytics as coupling caps and they are 25 years old. I did deal with instruments whose switching power supply caps (some of them high capacity "brute force" caps across rectifiers directly supplied by utility power), that lasted the full 25 years that we supported the instrument for. I suppose that one can either just replace all electrolytics. or check the power supplies for ripple.

[morzh]

Audio Classic are in the same place as McIntosh, Binghamton. They have a website and sell equipment, parts and service.
They still service these sets and their caps are marked with their name.

But they are not the ones who serviced it; as I remember, it was some shop in Texas. I should've saved the listing. It is kept for 7 years on eBay and it's been 8 years.
I guess I will call Audio Classics, to confirm. Those two smaller axial caps at the top of the phenolic board with bunch of axial film caps, the silverish ones, I guess are electrolytic caps. Hate to desolder to find out te values.
I am not worrying about contacts and resistors, the amp works fine.
But now that it is open,, I think I should finish the recap.

[morzh]

I contacted Audio Classics. They did service the unit in 2008 and then it came back for additional work in 2009.
I suspect there was someone else, as the Audio Classics go by the official diagram, wheres this mod is not in agreement with the schematic, but was done professionally.
Also heard many interesting things about things going on in McIntosh one year after its latest acquisition by Bose in 2024.
They sent me the latest schematic.


So, I have measured the voltages on the capacitors' outputs.

They are named after their respective voltages, measured at 117V AC input. After having made sure the power switch does not drop anything (it didn't) the measuremets were low.
So, I will put the "expected" and then "measured" values.

268V - 261V
290V - 282V
310V - 295V

The filament voltage (not given but should be 18V as it uses 1-1/2 tubes in series, each 6V) is 16.7V.

   
Above the snippet, the power supply of the C22. It is pretty ingenious.
First of, look at the Hi-V part. This is a voltage doubler. But you do not see it linked to GND. This is because they are stacking the voltage of the doubler on top of the filament power supply's voltage which is the Plus of C32A. So, you get some additional 20-25V out of it.

I intend first to replace the first Hi-V rectifier's caps, the C29, C30B/CD. Those are clearly old, the first two are 100uF 200V marked "Apollo" which, I suspect, have not been made at least from 1980s. If this brings the voltages to normal, I will stop; otherwise I will proceed to replace the multi-section cap C31A-C.
I also need to check the resistors. They are not necessarily the values that are declared, but I would like them to be the values that resistors themselves display. In-circuit they are not measured well somehow. I guess the residual voltages, however small, do affect the DMM alot. I will go with the values that are there now, as the resistors had to be recalculated, and I do not want to mess with it: those who serviced it, clearly were pros.

[radiorich]

Hello Mike,
Yes, that sounds like a good plan for changing out C29-30.

Back in the 80s and 90s, I worked on a lot of high-end audio equipment, including McIntosh. I even bought a tube model from one of my customers, and I really wish I had held on to it.

Sincerely Richard

[morzh]

Many consider C22 the best classic tube pre-amp McIntosh made.


Actually I own two, but the first one I bought was the modern version. It s still a tube C22, still made in Binghamton, but the circuitry is updated. Tube-wise, they use 12AX7 and 12AT7 (output driver, less gain/better load capability). I bought it in 2016.
The one in works right now I bought in 2018, and this is an original one.

They had an intermediate one, made between 1996-1998, that was more modern, with CD position, balanced outputs etc, but looked same as the classic ones, Frank McIntosh Commemorative Edition.

The modern one has different panel side trims (straight, not peaked) and knobs that are flat-faced with black faces, whereas all originals are full metal, with cone-shaped faces.

I paid for the modern a bit more than what I paid for the original (I ordered the modern from a dealer in Red Bank). Nowadays the originals in good shape cost even more, probably went up 20-30% since 2018. At least judging by the eBay asking prices.

[TV MAN]

That's an interesting way to do things in the power supply. Stacking the windings. I also like the pilot lamp dimmer stitch. I may take note on my future builds. I also agree some of those caps look pretty old.

[morzh]

Other than the two Cathode Feedback caps, I did the power supply recap tonight.

Funny thing, the low-volt caps, that were probably replaced not so long ago (perhaps 8-9 years) show a tad better ESR and D factor than the new ones I jusrt bought (all good brands, Chemicon and Rubicon).
They are not that critical at all, but it is funny. I recapped them anyway, all new lytics.

Tomorrow will finish the Cathode ones, but I could measure the voltages before that.

[MrFixr55]

Yeah, wonder why they did that. True, they had some DC available to do that, but was copper all that expensive back then to save 18VDC net on the AC required of the B Supply?

It seems that voltage doublers for B+ became popular sometime in the 60s for TV. Seen it on a few Zenith color sets and others with solid state diode rectifiers, transformer or not. My Heath WA-6M Power Amp has one.

[morzh]

This is possible due to no power output. Doublers work where no current demand is high.
I used it in a portable Telefunken when converting it from 220V to 120VAC.

[morzh]

So today I did one final thing, desoldered one of teh Cathode resistors and measured across one of thos small electrolytics; it was exactly 101uF, which is the spec of the latest old series C22, so I left it be.

Then I went to re-assemble it back, and realized that despite the photos I took, I forgot some things. Well, figured them out.
Put it back in the rack.
I heard good difference in sound, mostly bass.

Now, tthe very reason I started on that amp was the Tape Monitor switch malfunction. I flooded it with D5 and worked it many times, then let it rest.
Well...this did not work. The switch still does the same.
Since I do not use this amp for tape recording, I will leave it be for a while until I find out what people do with these.
At least now I know how to take it apart (was not very obvious) and put back together. Also, next time I do it, I will need that foam, that holds the glass in that metal frame, replaced. This thing almost costed me the glass today (it fell, but over the table and I was able to catch it...and n ot to cut myself).

[radiorich]

Hello mike,
I agree—why replace it if it’s still good ? The electrolytic measured exactly 101uF, matching the spec of the old C22 series, so I decided to leave it as is.

Sincerely Richard