Advice needed on how to approach a C22 restoration

analog addict

analog addict

Glory or Death!
I never figured I would wind up with one of these, but it kinda fell into my hands at a fair price, so I bit the bullet and grabbed it. As demonstrated by the pix, it is in near mint condition cosmetically with just a couple of scratches on the top of the black case and some dirt and the interior appears to be completely unmolested with a full set of what appear to be original tubes. According to the seller it was an estate piece from a former German national and was only briefly tested before landing in my hot little hands. However, apparently only one channel is working, and I don’t know if the working channel is 100%.

So the question becomes how to approach the restore. I called Audio Classics before I committed to the purchase and Ryan the Tech told me that even though most of the front controls are NLA, they can all be rebuilt. So should I not even attempt to diagnose the issue before starting in on the restore? I would assume I need a complete PS rebuild along with a complete set of electrolytic caps. Are there any caps that don’t need replacing? I am going to take this slow and easy since this piece is as nice as any piece of Mc gear that has passed through my hands...Thoughts? Comments? Suggestions?


Untitled by analog addict, on Flickr

Untitled by analog addict, on Flickr

Untitled by analog addict, on Flickr

Untitled by analog addict, on Flickr

Untitled by analog addict, on Flickr

Untitled by analog addict, on Flickr
 
Last edited:
Register to hide this ad
I can handle the work. It's merely a bit of guidance since this is the first one of these I've seen. I've been working on 110s for over 10 years...
 
Looks to be in excellent condition, nice.

I will always recommend diagnosis & repair first, hard to do a proper restoration without a good baseline. You could "shotgun" the restoration if it has many problems, but likely in your case a good switch and pot cleaning with Faderlube will be all that is needed to at least get both channels working and get you started.
 
I would say to replace the 3 can caps (since they'll need to go anyway), those two little electrolytics, and the orange sprague, clean the controls, and try it on the variac (while watching the amp draw). It looks like all the Telefunkens still have vacuum so are likely to still be good, though you could test each one to make sure. If it were mine, I'd probably replace the selenium rectifier with a modern silicon bridge--there's a McIntosh service bulletin for this floating around--and check the bumblebees for leakage. You did well with this one--it looks very nice.
 
Roger that. Thanks for the tips. I will slowly accumulate the parts and plan my strategy carefully. I’ve found the service manual and technical bulletins on HiFi Engine, so that is covered. Despite the temptation to start on this, I still have a recalcitrant 110 on the bench with the PT loose from the chassis but attached by leads and a stubborn hum problem hopefully narrowed down to somewhere in the final/6U8 stage. Without the tuna circuitry this promises (finger crossed) to be a more straightforward restoration....
 
Dave G has been kindly tutoring me on some of the downsides of the tuner circuitry. If you were to compare the schematic of the 110 to the C22, you'd notice prolly 3 times the circuitry on the 110, 2/3rd of which is all tuna. The grounding has to be much more precise and obsessive compulsive because the tuner circuitry can pick up any ground loops that might be almost unnoticeable in a straight preamp. Also, you look at the power supply of the 110, and it is WAY more complicated than the C22, with additional filtering, not only to remove ripple, but IIRC, to also prevent stray RF signals from intruding into the tuner signal. I'll be glad (if and) when I can get mine done and out of my hair.

Heh, unfortunately I have a second 110 restored by Dave Shoaf that is also TU right now since the whole filament chain on the tuna side went out. Fingers crossed it's only a bad tube, but I think one of these will eventually find its way down the road, since they are starting to drive me nuts, and I will hopefully soon have the C22 to take its place....
 
C22 has a lot of controls that need to be cleaned (including those on the top panel that are always in the signal path even when you forget about them) every few years. If you have not cleaned all the controls yet, i’d bet that doing so will get the dead channel alive. Still, a full restoration is very much worth the effort.

Congrats and have fun.
 
Looks like somebody (maybe Mac?) fixed the grounding issue that plagues so many C11s -- of which the C22 is just a more refined version of but virtually identical circuit wise. The circuit is grounded at one of the four mount points for the low level jack place. In the C11, all four mount points are riveted -- three are isolated from ground, but one is not and is the chassis ground point for the audio circuits (not the power supply). Over time the one grounded rivet that provides the chassis ground becomes compromised to the chassis, and must be drilled out and fixed with an appropriate screw and nut -- it looks like that has already been in in this unit, or was a factory change anyway, so you're ahead of the ballgame with that one.

In your pics, the upper left can cap can be confusing if you're not familiar with it. Again, it is the same as used in the C11. It has three terminals to it, but only contains two caps. The extra terminal is dead ended in the cap so that it only acts as a tie point. Oh those twicky Mac engineers!

Dave
 
Thanks for all the tips. One more quick question - what cleaner is safe for the C22 front plate and glass? last thing I want to do is wipe out the lettering trying to clean it up.

And Dave, the absolute last thing I need with this unit is a wonky ground......

;-)
 
Alright, all the 110z's are fixed and running with one having gone down the road to help cover the cost of this unit. I am putting together a parts list using the schematic as seen in the following image.

Untitled by analog addict, on Flickr

The caps highlighted in yellow are the caps that look to me to be the ones typically needing replacement. First off, do I need to replace all of these? It was nice of McIntosh to provide a number of notes on the early vs later units, but unfortunately, none of the missing caps or resistors are noted on the early schematic, and I have a later unit. I'm not too worried about the resistors, but anyone know anything about C35 and C36?

Also, is there a voltage spec for the unmarked caps? I noticed the .47uF caps don't seem to be potentially exposed to any more than 150V, so would 200V caps work? I say this because I have a number of 200V rated Sprague paper in oil/wax 118Ps that would serve well in this capacity. Will 200V caps work for everything else except the coupling caps? The .01 coupling caps will need to be somewhere north of 300V, so I'm thinking 450V caps or better.

Lastly there are some smaller caps which may have an effect on the signal path which I would replace if necessary. These are C1, C2, C19,C20, C35 and C36, indicated by red dots on my schematic. Do they need to be replaced, and if so, by what? Silver micas or something else?

Thanks in advance!
 
if it was me I'd put the caps in the power supply, lower right in the schematic on the "double yellow" list and replace them right out of the chute to get the power supply running properly and safely, and then move on from there. Did you test the tubes or find a fresh set?

Then I'd look to replace power related caps in the rest of the circuit, and interstage caps that are seeing high voltages from, for example, one plate to the next stage's grid. Last other caps in the signal path that are not seeing a lot of voltage. I think as a general rule the old bumblebee caps should probably go but you might be attached to them.
 
Oops. I didn't even mention the PS caps because as far as I'm concerned, they get replaced automatically. I've already ordered the Authenticap for the 1000/1000 can. I'm gonna get a CE 50x4 and a 40/40/20/20 can for the rest of the supply and prolly use the extra 40uF section for the first filter stage. Anyone want to comment on C1, C2, C19,C20, C35 and C36?
 
I took a quick glance at the M&X service manual, it's got a parts list that id's the original recommended types. many ceramic, some silver mica, etc. I have a hard time seeing your picture but I think C1, 2 equate to C79, 80 in that manual, and it calls out ceramic. You can find the manuals on line and do the rest of the compares. I wouldn't replace the ceramics unless something was out of spec or wasn't working, that's just how I roll.
 
You need to upgrade the resistors to to reduce noise in the phono section, too. I owned a C-22 for 9 or 10 years that I bought new. And having attended three Mac clinics, Davie replaced the phono section tubes each time, replaced caps in the phono section and replaced all the tubes twice. He gave me the best of the old tubes and told me to keep them as spares incase issues cropped up. They did. I could get Telefunkens at the radio station where I worked for cost, so having new tubes was never an issue if I needed them. The 240's were the units they gave me the most problems. Not so much the 275's or the MR-71. It was a relief to get the MR-77 and C-28, except for the mis tracking vol control on the C-28 and keeping all the controls clean. Relief was in sight however. The C-29 I had for over 25 years. No issues ever. Just clean the controls every couple of years it seemed.
 
Thanks! And Bob, if you click on the pic and go to Flickr, you can zoom on the images.

EDIT: Bob, I did a search on M&X manuals, and came up empty. Could you possibly provide a link for me and those who follow afterwards?
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom