McIntosh MC-30 variations

Hi Everyone in this wonderful Forum!
After 20 years of pestering, a friend of mine gave me the two mc-30 amps that her late father had. I am blessed! As an EE and budget audiophile, this is a dream come true. I plan to dust off my VT theory and soldering iron (yes I'm that old) and get these amps serviceable while keeping them as near stock as possible.

Amp #1: MC-30, Type A-116-B, power trans. M-152-D, unity-coupled trans. M-150-C, aux. outlet.
Amp #2: MC-30, Type A-116-B, power trans. M-152-B, unity-coupled trans. M-150-B, no outlet.

On the web, I found schematics for #1. I also found schematics for an A-116-A, which seems near to #2, but with different transformers. I have not tried to reconcile either schematic with my actual amps, so can't say how similar or different they are.

I realize there are differing opinions on mods. I would be grateful for any answers to the following.

Does anyone know where I might find a schematic for #2?
If I choose to keep each amp true to their original design, how different do you think they'll be sonically?
Any cap or resistor value differences you're aware of?
Do you think automatically updating all the caps is a good thing to do?
If so, stick with caps as close to OEM as possible? Polystyrene?
Any lead on capacitor kits?
Suppliers (ie Mouser, Part's Express, or something else)?
If resistors measure okay, would it be best to leave them alone?
Both amps have Sylvania tubes throughout. Opinions?
These amps have not been powered up for at least 15 years. Assuming no
problems with caps, what cautions do you suggest?
Any issues with the transformers and moisture?
Bring up on a variac?

Best Regards, Mike

 

If its been 15+ years since last power up, I would not even try powering them up (not even on a variac) until a filter cap job has been done to them.

-Aaron

 

Don't forget to replace the selenium diode which is used in the bias supply....it is orange/brown in color and many mistake it for a capacitor. Replace it with a 1N4007...1A, 1kV silicon diode. You will need to adjust the value of the dropping resistor slightly to maintain voltage specs. We used orange drops(polypropylene) to replace all coupling caps in my sons MC30s. Be sure to replace the filter caps as well(electrolytics).

One other thing, the red band on the old diode is the CATHODE. Be sure the banded end of your new diode connects where the red end was installed.

Regards, HG

 

I kind of figure if the guy is an EE, he probably knows his way around a basic tube amplifier pretty well....

 

Welcome to the forum, and congratulations on your good fortune! I'll second an earlier bit of advice: Terry DeWick is tops at McIntosh repair/service, and a very nice guy to boot.

Please do keep us all apprised of your progress with the MC-30s.

 

Thanks for all your advice and opinions!

I plan to keep these as stock as possible, perhaps modding down the road.

I plan to work on these myself. Between work and home, I have access to a fair ammount of equipment and have built SS amps (Super Tiger variations) in the past from scratch. I've wanted to renew my audio hobby for a while now.

I definitely will replace PS caps before any power is applied. Thanks for the hint about the selenium rectifier marking. In addition to being backwards, it serves to remind me to take it slow and educate myself.

Humbly yours, Mike

 

One of my babies is with him right now and I'm pretty excited about it

he's getting my other baby later this year as well.....

 

Mickey,

Lots of info on the aforementioned Audiokarma McIntosh forum for restoration of the MC 30's. Congratulations on the amps and please post back with what work you perform, and impressions.

Paul