MA 6100

[PhilA]

Howdy.

I just picked this MA 6100 up. Looks to have been fairly well cared for then put into storage outside. This afternoon it was sitting in the trash, upside down on a pile of old carpet (sadly rained on) so it found a new home.

It is not bad, cosmetically. The case is pretty good though the front litho has bubbles in it that warrants investigation.

First up, going to hunt for a manual. Second up try figure out the cage release mechanism. Inspection then onto the Variac, I think.

Worth the effort? Thoughts?

Thanks

Phil

 

[Pio1980]

Very much worth renovation.

 

[Mike Gibson]

Push the silver buttons in and release quickly until you feel them release. They are below and to the side of the bottom two knobs. Some folks don't use a variac on SS gear. Just a thought.

 

[PhilA]

I put everything with a linear supply on the Variac. Usefully, mine has a shunt with an ammeter inside.

Thanks for the tips on the release mech.. It would pull out a little bit the buttons would stay level with the wooden case as it felt like I i was pulling against a spring.

Phil

 

[PhilA]

Ok, got it all out. Preamplifier stages are toast, power amp stages seem to mostly work. Front panel has delaminated due to being rained on, pity.

Might pull the boards, they've been "worked on" in the past. Rather a lot.

Phil

 

[PhilA]

The release mechanisms were loose in their fixings and tight due to age, but it came apart eventually.

Appears to have been last properly serviced in 1975

To be honest, I've opened up to find much worse than this before.

This appears to be the caliber of the repairs on most of the cards.

More to follow

Phil

 

[PhilA]

Took it to bits to clean it up.

Chassis came up ok. Bit of surface rust but nothing serious.

Went over the connectors, switches and pots with a little Deoxit.

Brought up gently on the Variac, with a couple of sacrificial speakers. Preamp stages don't appear to be working. There's signs of heat stress on a few components.

Front panel has the wrong lights fitted. Squeezed a fair bit of water out from the transfer but it'll never be 100%, sadly.

Reassembled it and will carry on, hopefully with a manual.

Phil

 

[c_dk]

You need the jumpers between the preout and main in. The originals were horseshoe shaped, a patch cord works in a pinch.

 

[c_dk]

The release mechanisms were loose in their fixings and tight due to age, but it came apart eventually.

Some techs refused to pull out the production leg holders.......have seen way too many half ass solder joints like this over the last 40 years.

Appears to have been last properly serviced in 1975

To be honest, I've opened up to find much worse than this before.

This appears to be the caliber of the repairs on most of the cards.

More to follow

Phil

 

[PhilA]

Aha, so it's not jumpered internally. That'll be why. I didn't get a schematic yet.

Every single transistor has been soldered in

Phil

 

[c_dk]

You have a bunch of caps to upgrade and some detail work to get it singing in tune again.....well worth the effort to sweat out the details as outlined in many past posts.

 

[PhilA]

The first stages of the power amplifier look, by the dirt on the top grille, to run hot.

Hooked up properly it does play so yeah. Work ahead with this one.

Tempted to try find a new front panel for it. That can definitely wait though.

Phil

 

[PhilA]

Manuals now printing, courtesy of http://www.berners.ch/McIntosh/en/Matrix.htm

Going to have to dig to find transistor replacements.. it's currently a mix-n-match.

--Phil

 

[PhilA]

Cleaned the case up and re-oiled it. Looks a bit better now.

Phil

 

[PhilA]

Spent yesterday evening starting to go through the boards, easy stuff first. Checking resistances and replacing the ones outside of their 10% tolerance. A surprisingly large number have gone bad. Method is to measure in-circuit.. if it doesn't look right, lift a leg and measure. If bad, find the best (closest to spec) match from my new resistors and replace.

The phase shift board was bad, with all but one of the resistors having drifted high. For instance, a 47k measuring 58k would be replaced.. probed each new resistor to find the best one (all new replacements going in are within 2%).

Right channel preamp wasn't so bad.

Had a quick listen with only those changes and it's already better. Less muffled. Other boards up next, but it was getting late so I buttoned it back up.

I give it.. three stars out of five, cosmetically.

--Phil

 

[PhilA]

In wrestling the thing into the cabinet, then going look at Google, it wold appear someone decided this one was better off without its' base.

Oiled the release mechanisms because they jammed up again, locking the thing into the cabinet. Working on a cap list for it.

--Phil

 

[PhilA]

Continued onward and upward last night. Checking resistors. Surprising how many are well outside spec.

Getting there. Other power amp board next up. Already sounds better. Doing the preamp boards really made the most difference. All the resistors are now within 5%, been checking and picking the best ones to go back in to keep both channels as balanced as possible. Y'all said it was worth the effort, so there's the effort going in!

--Phil

 

[62caddy]

Tip: If the cabinet release mechanism is stubborn, it helps to twist the Panloc buttons a bit.

It is always nice to see old forgotten Macs rescued. Good luck with it.

*Both Audio Classics and McIntoshaudio sites are showing new MA6100 glass faceplates in stock.

 

[N8Nagel]

Howdy.

I just picked this MA 6100 up. Looks to have been fairly well cared for then put into storage outside. This afternoon it was sitting in the trash, upside down on a pile of old carpet (sadly rained on) so it found a new home.

It is not bad, cosmetically. The case is pretty good though the front litho has bubbles in it that warrants investigation.

First up, going to hunt for a manual. Second up try figure out the cage release mechanism. Inspection then onto the Variac, I think.

Worth the effort? Thoughts?

Thanks

Phil

Are you serious? It's McIntosh. Even if you decide it's not for you it's definitely worth getting it running and selling, because a) someone will want it b) it's a shame to see any nice old gear get trashed and c) you'll probably be surprised how much you get for it, Mc gear holds its value. Who throws out stuff like this?

 

[PhilA]

Well, it's my first foray into McIntosh gear. I've rebuilt a couple Pioneer sets in recent years. This is quite different.

I just need to try locate the sheet metal for it. The reason the panloc sticking seems to be the missing base. Placing it on end and letting it settle appears to be the current trick.

I am going to hunt for the various missing bits, and until then check it out with a fine tooth comb.

The preamp boards have been hacked about with though.

Phil