MC-275 Restoration

E

evilE

New Member
Hello all,

I have just inherited a rather tired MC-275. The poor amp has seen many years of use and been through a house fire in 1978. I'm not certain where or when she was first put into service, but I know that in the '70's she was part of the Grateful Dead's "Wall of Sound". After the Dead retired her, my dad picked her up and she became his main hi-fi amp until the fire. The amp suffered only minimal smoke damage, so dad put her in the shop as a test amp, where she worked daily until last week. Dad just retired that part of his business so he handed me the MC-275 and a pair of Nelson-Reed 8-04's.

The MC-275 has been modified with XLR and 1/4" connectors (I assume when in service with the Dead). I plan to return the amp to "stock", so I need a few pointers:

My specialty is metal work, so I'll patch the holes in the chassis, machine the OEM holes back in, and have it re-chromed. I'll also handle the paint work. I also have a background in electronics, so I'll be disassembling/reassembling the old girl. The big questions are: Has anyone made a screen for reprinting the chassis lettering? Are there some good mods or circuit revisions that I should consider? Is there a wiring diagram or great picture available (I already have the schematics, but wire path is important and my 275 has been changed)?

Also: what are people using for replacement power and circuit caps? Should I replace the rectifier?

Lastly: How are the small tubes labeled? Is it V1-V7, front to back?

I appreciate any info you can pass along!

Thank you,
Ethan
 
Register to hide this ad
I would leave the Dead's Mods untouched. Probably worked on by Bear himself. Priceless historical value if true. The Dead's mods were done right and probably improve the sound and noise level.
 
grateful said:
I would leave the Dead's Mods untouched. Probably worked on by Bear himself. Priceless historical value if true. The Dead's mods were done right and probably improve the sound and noise level.
Click to expand...

Yes, the mods were undoubtedly performed by Bear, as he and my dad go way back and co-developed much of the Wall Of Sound. But, this amp needs help. The XLR, 1/4" and other I/O jacks are either not hooked up or painfully degraded. The selector switch is non-functioning, and one of the input pots is missing and associated wiring left soldered together and dangling. Power caps are original and the power supply has fried at some point. The Thermistor is split in two and that circuit bypassed. The transformer covers have been sprayed with a rattle can and chrome turned to rust. Last, the terminal strips have been replaced (badly) by banana sockets that are worn out and corroded down to base metal.

Normally, I would agree with you, but in this case I need to return the amp to OEM, just to make it easier for me and further generations to service the thing. If I had Bear's schematics and reasoning behind certain mods, I would consider leaving it, but Bear is a little hard to get ahold of and he lives in the land down under. At this point, I'm on a rescue mission.
 
How about John Curl, or is he your dad?:-)
I'm with Grateful; I'd keep it as-is and replace components like-for-like as need be.
 
Yes, Who is your dad ? I know the dead liked the balanced connections for ease of hookup and noise rejection. The other mod is probably mono operation. They even modified guitars for all balanced lines.
 
grateful said:
Yes, Who is your dad ? I know the dead liked the balanced connections for ease of hookup and noise rejection. The other mod is probably mono operation. They even modified guitars for all balanced lines.
Click to expand...

I second that question. :yes:

Other notable folks who worked on the Wall besides Bear and John Curl include Mark Levinson, Ron Wickersham and Jim Furman. The MC 275 was not used in the final Wall of Sound in 1974, which used MC 2300's exclusively. Tube gear was retired by mid-1973 at the latest because of reliability issues with the constant transport of touring.
 
Would be interesting to take pics of your amp before and after restoration.

Sounds like a big project :yes:
B.
 
My dad is Rick Turner... Google him. There were quite a few great minds involved in the Wall.

I'll take some pics of the amp as it sits and post them when I can.

My present plan is to test the amp, replace the power caps, clean up the loose ends, and run some music through it. If it sounds great I may just leave it as-is. After all, it's a good conversation piece as it sits, battle scars and all... At the end of the day all I really want is a great sounding tube system.

On a side note, I remember Bear, Ron, and Jim well. In fact, I worked for Jim at Furman Sound as a bench tech in the early '90s.
 
Silkscreening the text on vintage McAmps comes up often and it's a problem. As far as I know, there is no one actively doing this right now (for a 275, anyway) so it has to be done one-off, and, by someone that knows what they're doing. Think in terms of a few hundred dollars.

Murray
 
Sounds like an interesting project. I would get a copy of the service manual first as it has a lot of the info you will need. Filter capacitor kits for MC275's are available on Ebay and I'd imagine elsewhere on the internet. Changing the capacitors in the signal path seems to be a topic of debate with valid arguments both for and against changing them. Which brand of coupling caps to use would again be another matter of opinion. There was a lot of interesting stuff written about MC275's being used in pro sound applications in the Mcintosh book that came out a while ago.
Mike
 
Yep. sounds like a road amp. Replace the defective parts and use it in its' current cosmetic condition is the best idea. Terminal strips, thermistors, and caps are available. The signal caps and the close tolerance resistors should all be changed so you don't risk damaging the transformers.
If you want a clean MC275 it is best to spend the money on a super clean example or just buy a new one. Wally Hider had the clean ones as they just set in the wall of his studio.

Thanks,
Ron-C
 
evilE said:
My dad is Rick Turner... Google him. There were quite a few great minds involved in the Wall.

I'll take some pics of the amp as it sits and post them when I can.

My present plan is to test the amp, replace the power caps, clean up the loose ends, and run some music through it. If it sounds great I may just leave it as-is. After all, it's a good conversation piece as it sits, battle scars and all... At the end of the day all I really want is a great sounding tube system.

On a side note, I remember Bear, Ron, and Jim well. In fact, I worked for Jim at Furman Sound as a bench tech in the early '90s.
Click to expand...

No need to Google, your pedigree is well established. :yes:

I look forward to your progress reports, photos and listening reports. And please thank your father for all he did to support the music. :thmbsp:
 
You must log in or register to reply here.
Back
Top Bottom