Ampex MM1100 PSU Recap - Questions

[bluezplaya]

Hey everyone, it's been a hot minute since I've posted on the forum. A few years back, I purchased an Ampex MM1100 24 track machine from a guy out of Nashville. The previous owner had it set up as a 16 track and the two spare card cages and other 8 channels of cards and parts came with. I've also got a 24 track headstack for it. When I bought it from him, I thought he told me the PSU had been recapped at some point, so I just checked the voltages and they were good, and went to recapping the channel cards, swapping out C32 on the repro, switched to WIMAs on the EQ cards, etc. Anyways, 12 or 15 sessions and happy customers later, it's still running great, sounds great, have run it at 15 and 30. However, I decided to finally get around to setting it back up as a 24 track with all channels in, and just being able to swap the headstacks between 16 and 24. I pulled the card cages out and saw that I need to recap the electrolytics in the back of there, AND, when I got around to the back of the machine and took the back panel off, the PSU has never been recapped (or not in a long time).


I've got the manual with all the schematics and parts list, and after putting my eyes on the capacitors, I made note of the values needed to swap out for new. But before I go diving in searching on Mouser or Digikey, I wanted to ask if anyone has recapped an MM1100 PSU recently and can give a heads up on where to buy, if other capacitance values will work in place of something that may be unobtainium, etc

The main power caps are two 10000uf/75v cans and two 1400uf/75v cans. I can get the bigger ones from Mouser but can't seem to find the 1400uf.


And there are two cans in the back of each card cage that are labeled '250 to 500MFD / 50v' and are listed in the schematic as 'C2 QUAD, ALUM, 500UFD, 50V'. These cans each have 8 solder terminals on them, and wires connected to only 4 of them. Where the hell do I source these??



Also, the Motor Drive Assembly card has two 1uf/600v capacitors that don't look like they are polarized. Should these be replaced?

I think I can find the other values needed, it's mainly these larger can capacitors I'm trying to find. Any help is appreciated.

 

[Brian Roth]

It's been eons since I worked on one of those so all I can make are some general comments.

Before replacing those big 75 V caps (likely to cost a fortune....lol) use a capacitance meter to see if they are still in spec. Probably also good to measure ESR as well. Those "computer grade" caps with the screw terminals can have a LOOOOONG lifespan.

Looking at those quad cans, the outer-most four solder pins around the perimeter are all a "common negative" for the four sections in the cap. The four lugs that are more towards the center are the positive terminals for each section. At least that's what it looks like to me.

Good luck finding a direct replacement in year 2024. You may have to use four individual caps and concoct a method to install them.

Bri

 

[radardoug]

I would not bother with the big supply caps, I have a 1200 and they are fine. Some of the others though you need to do.
I would do the record amp caps. The output cap particularly as if it goes it puts dc on the record head. And there is another cap in there that badly affects record gain when it goes.

 

[beatnik]

I have sent you a PM about spare card cages, I would be interested in buying one of your spares. Please let me know. Thanks

 

[JW]

Update? This looks like a stinker of a job, that I unfortunately have in my future as well. I have a MM1100 that hasn't been powered on in years. Starting to wonder if I can borrow a VariAC from sowewhere. Or should I just cowboy up, and flip the switch? Will replace that tant on all record cards first.

 

[radardoug]

Good luck with that! A variac would be good, but you need a big one!