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MC225 arrived, restoration project

OneyedK

OneyedK

Active Member
My MC225 has finally arrived, customs cleared me out so sourcing parts will go slow.
Time to do some preparations...
I did my homework, so hints and tricks for the MC225 are gathered in one document.
Still value any remarks and suggestions from you all!

A litte question to start, is there any way to know when this amp is made?
Serial number (on box, on inside of chassis and on top side of chassis) is 270C7.
Inside, there's another number stamped: 591160
and engraved in the chrome is: 01057

Pictures before I get started: (hope this number of pictures is not a problem)

Closed look:
IMG_5745+.jpg


Open look
IMG_5750+.jpg


Sideview with serial number
IMG_5751+.jpg


Overview with all numbers stamped.
IMG_5757+.jpg


Mainboard resistor side
IMG_5758+.jpg


Doubler cap
IMG_5760+.jpg


Input configuration
IMG_5762+.jpg


More input configuration
IMG_5763+.jpg


Mainboard cap side
IMG_5765+.jpg


PSU board, resistor side
IMG_5768+.jpg


Cap can config
IMG_5774+.jpg


Where the CL-80 will go
IMG_5777+.jpg


PSU board, cap side
IMG_5784+.jpg


Thanks for looking!
 
Last edited:
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The serial number range for the MC225 is from 100C1 to 700C6, so yours (270C7) is an earlier production unit. Total production was 5,591 units.

These were built between June of 1961 and August of 1967. That is about as close as you are likely to nail it down.

Larry
 
Thanks for looking![/QUOTE]
Wow! The getter flash on the tubes is bright,and shiny. That is suggestive that the usage of this amp was extremely light during its lifetime, assuming those are the original tubes. No sign of any dust on the internals. You have a real 'time machine' piece there!
 
Don't know if the tubes are original, but I guess not. The 7591's are GE coin base, no McIntosh label there. The fact that they are bright and shiny could be the 500W softbox lighting them ;)
12AX7 is a Telefunken, didn't examine the AU's and BH's yet.
And the clean internals is the result of what proper use of a can of compressed air can do ;)
Only have part of one day a week to work on the amp, next up will be checking the resistors to see if they're still close to their original value.
Trying to get to know the little beast before ordering the parts. I know if I hurry, I miss things...
 
Nice.

Check the resistors R10, 11 and 12 on both channels. They always tend to drift with age.
 
Thanks! Common cathode and anode resistors of the PI.
Was planning on replacing the "bad" resistors with Takman REY50 (0,5W), unless somebody would suggest using 1W in the mentioned spots?
 
OneyedK said:
Thanks! Common cathode and anode resistors of the PI.
Was planning on replacing the "bad" resistors with Takman REY50 (0,5W), unless somebody would suggest using 1W in the mentioned spots?
Click to expand...
I used takmans in my MC30s with excellent results. Good luck with you project!
 
Beautiful and pristine condition MC225 -- I'm envious. I recently refurbished my MC240's power supply using Authenticap can caps, fast/soft recovery diodes, a larger capacitance Nichicon VX cap bypassed with a 5uF metabolized Polypropylene film cap on the bias supply, and Ohmite Brown Devil vitreous enamel wirewound resistors. The bias supply parts including the caps and diodes were part of Jim McShane's bias supply rebuild kit. I also replaced the cathode bypass caps on the 12AX7 in the input stage with Sprague TVA Atom electrolytic caps. The results have been fantastic as the amp is livelier and more articulate, but maintains that rich, smooth tone. The amp has more of that holographic magic than before in regard to imaging and size of soundstage.
 
rhing said:
Beautiful and pristine condition MC225
Click to expand...
I'm still contemplating if this is a curse or a blessing ...
I was planning to go "all in" and replace just about everything,
now I want to tread more carefully, leaving as much of the original parts as possible...
On the same time, I don't want to end op with an amp that needs to be taken care of every few moths :s
(Authenticaps already ordered directly from Jan in Germany)
 
I would only replace the components in the signal path as needed. There is something special about the original voicing of these vintage McIntosh tube amps that can get lost when replacing a lot of the original components. For my MC240, I replaced the critical power supply components like caps and diodes and the cathode bypass caps. Everything else tested fine, so I left it as original as possible. Interestingly, the power transformer doesn't even get that warm anymore. In fact, the output transformers get warmer from the heat radiating from the output tubes. If I had to replace any resistors, I was sticking with NOS Allen-Bradley Carbon composition resistors. For any bad signal caps, I was going to replace them with NOS Russian K40y-9 PIO caps that I purchased from Jim McShane. Unfortunately, the power tubes are not original, but I am still able to enjoy the finer nuances that this amp provides.
 
Is there a valid reason to replace the stock silicon diodes? The selenium one will be replaced with an UF4007 (I don't stock the regular 1N4xxx).
For the coupling caps, I was planning on the K40y-9's too. Maybe not for the coupling caps of the output tubes, as I like the Mundorf MCap Classic. Great sound without being too big to fit.
But if the Brown Dogs are still good, I'll leave them in place.
If I have to replace resistors, it'll be with good quality metal films.
Not that I dislike carbon comps, but I prefer the reliability and long term stability of the metal films.
 
Dit you use those Dale resistors for a specific reason?
And why did you use the K42's instead op K40's?
 
Not really: they are very good film resistors and supports the right voltages.

The K40 were too big to fit all. And the K42 are hybrid, even better.
 
OneyedK said:
I'm still contemplating if this is a curse or a blessing ...
I was planning to go "all in" and replace just about everything,
now I want to tread more carefully, leaving as much of the original parts as possible...
On the same time, I don't want to end op with an amp that needs to be taken care of every few moths :s
(Authenticaps already ordered directly from Jan in Germany)
Click to expand...

rhing said:
I would only replace the components in the signal path as needed. There is something special about the original voicing of these vintage McIntosh tube amps that can get lost when replacing a lot of the original components. For my MC240, I replaced the critical power supply components like caps and diodes and the cathode bypass caps. Everything else tested fine, so I left it as original as possible. Interestingly, the power transformer doesn't even get that warm anymore. In fact, the output transformers get warmer from the heat radiating from the output tubes. If I had to replace any resistors, I was sticking with NOS Allen-Bradley Carbon composition resistors. For any bad signal caps, I was going to replace them with NOS Russian K40y-9 PIO caps that I purchased from Jim McShane. Unfortunately, the power tubes are not original, but I am still able to enjoy the finer nuances that this amp provides.
Click to expand...

I hear this said and repeated quite a few places, with no real evidence for it. Precious few people have done anything approaching direct comparisons pre/post a proper restoration. I am one who has, and I say if you have the skills to do so you'll never regret fully refreshing the amp.

I had a pair of essentially bone-stock MC60s. They worked when I bought them. I replaced almost everything in them anyway; along the way I found that the majority of the components didn't meet spec anymore (those that still did, may well drift out under load - I'm looking at you, carbon comp resistors). You can see my component choices in my build thread with pictures. When at long last they were done, they sound incredible - no doubt better than before, and I was impressed at stock.

These amps have a reputation, but you'll only be sure you're hearing what McIntosh intended if the components are in spec. For those who want an unused time capsule, fine. For everyone else, out of direct experience I recommend a full overhaul. You'll be glad you did.

The are only select exceptions to this which should be retained:
  • Transformers
  • Black Beauties (Sprague 160P series), if present
  • "Plate chokes" between driver tubes
  • Wiring
  • Physical hardware
 
I pretty much agree with all what you said SilverTpt999.
I have done it on 225, 240 and lately 275.
However, some "black beauties" 160P do leak under rated voltage even if their capacity in as specified, so don't assume they just are all good.

I always do one channel first so I can compare sound wise with the vintage one. Well there is no comparison. It's like you lift a layer of cotton from your speaker.

So I now replace all, regardless. And I always end up having the voltage right on target.
But I do check the value of each component before installation: once again I had surprises.
By doing that, you know the new components you installed are on spec.

My 2 cents.
 
Just FYI, date codes on the 12BH7 tubes (which appear to me to be original to the amp) would indicate your 225 was produced in late-1962.
 
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