McIntosh C8 & C8-S Preamplifier / Compensator Restoration - Part 1

Bench testing a complementing pair of McIntosh C8 & C8-S preamps / record compensators. Doing a thorough walkthrough and building a parts BOM. These are a match for a set of MC30 tube amplifiers that will be shown in a separate video.
Please watch the teaser video associated with the matched set of preamps & amplifiers:

Hope you enjoy!
Stay tuned for Part 2 once parts arrive.
Mark

[NickP]

No matter how many parts need to be replaced, that’s a timeless and beautiful piece of tube gear and HiFi history.

[gizmothewytchdoktor]

it's good to see where and why mcintosh got their reputation for quality of build by seeing the internals of these units. thanks for the peek!

[preiter]

Very clean construction on these preamps. Thanks Mark for the detailed video!

[adamwolfram]

This is a nice, thorough video. Thank you for taking the time to make it! I'll be restoring a pair of C-8 preamps soon, and this video is a nice primer for that. Plus, it got me geared up to do the work! : )

[jeb]

Thanks mark. I’m learning more and more and I think things are beginning to soak in. I like the schematic walk throughs

[chrisvinicombe]

I'm going to enjoy this series 😊 the preamps were surprisingly good, hopefully the power amps are too 🤞
I had a good chuckle with the resistors are capacitors mix up half way through thanks.

[desmondroche]

As I purchase a lot of my records from thrift stores and swap meets, I come across a lot 78’s and monophonic Lp’s pressed with non RIAA equalization curves. So I’ve long wondered whether a phono preamp with adjustable equalization curves, like the McIntosh C8 ‘Audio Compensator’, would greatly improve the playback of these non RIAA records. There are some aficionados of these records that even advise playing back mono records on single speakers with era specific monophonic cartridges (e.g., GE VR2’s) to get the best sound. That’s why I’m particularly looking forward to the restoration of this C8 + MC30 combo, and am hoping that when you film a demonstration of the sound of the fully restored units (which you usually do), you’ll test it playing a 78 or non RIAA Lp through a single speaker with a monophonic cartridge, if that is at all possible. I know this is demanding, and only to satisfy my esoteric curiosity, but it’s unlikely I’m ever going to come across a fully restored C8 and MC30 in my neck of the woods. And I suspect some other record geeks out there among your viewers share my curiosity.
P.S. The underground cartoonist and lifelong 78 collector R. Crumb apparently uses a McIntosh C8 to play back his 78’s, according to a description of his system on Lenco Heaven.
P.P.S. In 1985, The Audio Amateur (IIRC) published a series of articles by Gary Galo (IIRC) about restoring a McIntosh C8 for ideal playback of records with non RIAA equalization curves. Perhaps there might be something of use to you there.

Even if you can’t meet my request, thanks anyway for all your excellent videos !

[thermionic]

Those brightly-colored capacitors are the bees’ knees!

[davidanderson]

I need to rebuild my C-8/C8S and MC-30's and this was very helpful. Thank you! It seems to me the C-8 cannot be plugged into AC without the MC-30 amp hooked via the umbilical cord, or you buy the McIntosh power supply if not using a McIntosh power amp because the MC-30 has part of the power supply needed for the C-8. I think I am right about this, but not positive. I figure they sold the separate power supply for a reason! If this is true, I hope you are aware of it and that you will mention it in the next video. Thanks again and I look forward to future videos

[curtisgriffin]

Excellent video Mark. Great tips on what to look for in troubleshooting. Do you also plan on doing a full scan on the tubes since the quick scan is at one set voltage and not the entire range the tube has to operate at? Love to see more restoration vids in the future!

[EngineeringVignettes]

I'm willing to bet that the _bumble-bomb_ that went off was the death cap... I have had other radios that suffered the same fate.
Cheers,

[jerryjohnson]

do you know the color of the outside case of the mcintosh mx151 need to restore it

[eddieh]

I am currently restoring a McIntosh A-116 and C-108 combo. The A-116 is a predecessor to the MC30 that uses 6BG6G output tubes. I believe the C-108 is also a predecessor to the C8. The C-108 has a number of tubular ceramic capacitors wired to the slide switches in the bass and treble compensation circuits. These look like resistors but have 5 color bands instead of 4. The values for these are in picoFarads. I did not notice these at first until I started wondering why there were 40 capacitors in the C-108 parts list, but I was only replacing 21 bumblebees and 6 electrolytics. Just curious if the C8 has the same tubular ceramics? From one of the shots in the video, it appears that it does. You mentioned leaving the ceramic disc capacitors in place unless you find a reason to replace them. I plan to do the same with the tubular ceramics in the C-108.

[mattgring]

Awesome! Just fyi @ 22:00 you say capacitor when referring to the resistors.

[MassimoTava]

If the engineer that designed this had access to today’s parts list, what would they have used?

[rickg]

Hi Mark.. What type of caps do you plan to use as replacements for the Bumblebees?

[russellhltn]

I can understand using DC for the filaments, but why a voltage doubler? That seems like an odd choice.

[James-hbee]

Wonderful video, but I cringed every time the edge of the faceplate scraped across your work surface. Ever thought of getting a rubber pad to work on. Just a thought.

[russellhltn]

I was going to point out the times you called resistors "caps", but I lost count. Must have been a late night proofing session.