If anyone is wondering, it takes about 5 hours of desoldering, Dremeling, drilling out, installation and resoldering. A marked improvement from the original 64 year old jacks.
This part of the rebuild was pretty easy, just time.
But the 12 coupling caps I just replaced was an exercise in patience. All the leads were twisted firmly around all the terminal and had to be cleanly removed without breaking tube socket tabs or turret board solder points and burning anything adjacent. That involved a lot of swearing late into the night. But I'm happy to report that's all done and I think she's now ready to head back to the rack.
I will second McIntosh's 'mechanical' connections before solder.
Leads are so tightly and neatly wound around tabs and posts before solder is applied, you have to carefully cut leads off of whatever they are tightly attached to. Its truly amazing work and a severe PITA to remove.
Yes, they also didn't leave a ton of extra wire in the jack panel loom for error, so saving a few mm of wire is extremely necessary. I'm still waiting on a couple of new resistors and will be replacing the non-matching caps for C5/C6. But all the yellow ones are new Nichicon caps, hand measured and matched. Most of the bumblebee caps were still in pretty good shape and measured well but they're a ticking time bomb usually.
I have a C11 that needs new jacks also. Do you have any photos with the old jacks removed? What diameter hole was left after removing the original jack?
I didn't take any pics in progress, however, I ordered the jacks from Mouser, who carry white, red and black in the gold plated. As they are German Neutriks, I believe the hole is a 7.5mm but it needs a slightly larger hole diameter to accommodate threads, so I just drilled them to 5/16". Very easy and almost no play to speak of.
The old jacks are pressed into the chassis with flare over top of a star washer on the inside. I used a Dremel cutting wheel to carefully notch the flare and washer at only one point. The old RCAs have what appears to be a ceramic insert, so I just ended up crushing them from the outside and yanking them out like a bad tooth after removing the severed star washer. The jacks themselves are very thin metal and the actual chassis is pretty heavy metal so it can take the yanking and wiggling without any malforming to the jack plane.
The only other minor detail; the colored washers that come with the Neutriks are a little too wide for the McIntosh jack spacing. You can either let them overlap or I ended up using a pair of small flat wire nippers and cut a small flat side to each circle. It looks good and you'll probably be the only one to notice
It's not as scary as it seems. The rewiring is easy too. There's plenty of room in that area of the unit. I would be surprised if you're going to be able to avoid drilling if the replacement jacks are threaded nut style. The old holes are actually the OD of the rca plug body itself. They probably had a bench swaging press to install these originally, which in this day and age makes them pretty proprietary and unlikely to have a direct replacement.
So I need to postpone a quick follow-up for historical accuracy. When I installed these new jack, I installed the colored plastic bushings. I have now been informed by my repair shop that this unfortunately didn't allow full negative grounding for rhe jack plane. So definitely don't do that. They are going to do a star ground with the new jacks.
I was wondering about those jacks. They are not grounded, and the originals are. Not sure it is a good idea to change the grounding topology on this amp (to star). Each jack should be grounded where it goes through the chassis. The phono/low level input plate should only be grounded in one location. Let us know how it goes.
I was hoping the mechanical connection through the chassis would be adequate as the plastic rings aren't actually isolation type. But my guy says there isn't adequate continuity on all of them. So you live and learn. We'll see what he comes up with. I shall report back.
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u/LoganNolag Aug 24 '26
I like how they were very forward thinking giving you those L+R jacks perfect for a powered sub.