Category Archives: McIntosh MA6100

Multi-cap can

Had a bit of spare time and inclination today so I took all the connections off the back of the McIntosh after labeling the wires. That’s a task in itself.
Removed the old multi-cap can. Took to the base of it with the Dremel. I had wanted to retain the original look of the capacitor as the top of it sticks through the chassis. The old brown heat marks show the point where it shows. The Dremel cut is well below the visible line.

dermelled

Mallory’s finest. Still in surprisingly good physical shape.

can dissected

Cleaned the dregs of tar out of the case after softening it a bit in boiling water.

tarpit

Removed the old capacitor wad. Four new caps to fit inside. It would appear Nichicon listened to the classic audio crowd because these are common values and voltages the the era, designed to fit inside old cans easily.

new bits

Fitted the caps all in place. They fit nicely. Actually over the spec of the originals on voltage and temperature. They should last.

newcaps

Had to drill the base to pull the leads through. Kept the original markings intact.

square triangle semicircle

Glued back together it looks nice. Gave it a bit of a buff up with a bit of metal polish.

restuffed

Looks neat back in the chassis. Sitting listening to it now and it’s running happily.

Matchmaking

I recapped an old Dell power supply, as it has some useful voltages (-12, +12, +5, +3.3) and was more than enough powerful (160W) for most of the projects I do. Added a small load to the +5 rail and the voltages stabilised, that’s the light bulb.. spent a bit of time and built up matching circuit on Veroboard.

messy

Initial testing was good, so tidied things up a little.

board

Set about measuring transistors to see the Vbe of each. Matching at 72F to within 2mV.

measuring

Did 100 of them, they are surprisingly close (all within about 5mV) so I have more matched and/or similar pairs than I thought! That’s good, means all the transistors installed can be identical.

McIntosh recap

Along with the parts for the Marantz, I bought a set of parts to make a transistor matching circuit. I bought 100 of each NPN and PNP silicon to match up accurately, as that’s what the spec calls for on the amplifier boards.

recap preamp

I recapped the preamp boards first. All ultra-low impedance capacitors, as per the original spec, though these are aluminum rather than tantalum.

regulator

Redid the regulator/phase-shift board.

compare

As a comparison, I put the power amp boards side by side, the left one done, the right one yet to be.

power amps done

As if by magic, the power amp boards are recapped. I bought some very tall and thin caps to restuff the multi-cap (4 capacitors in one can) because it growls a bit on power-up. I want to keep the appearance of the original can because it’s a prominent feature of the top of the case when you look at the chassis. It’s polished aluminum. That’s up next. I’m going to save up and get the main filter caps at a later date because they are rather expensive ($25 each).

1866 for 6100

I bought a new set of #1866 bulbs for the McIntosh, as most of them had burned that illuminated the front panel.

panel off

The old foam surround going around the buttons had dried out and was turning to dust.

vacuum

Too the vacuum cleaner to it, it all just disintegrated and fell off.

peel

That left just the original sticky backing, which peeled off.

foam

A new length of foam that I’d bought for things like this came into play.

new foam

Created a new surround for the buttons following the original pattern.

hot

The original bulbs run quite hot. The speaker ones were not even brightness, so I fought for half an hour getting them out.

nice

All buttoned up, new bulbs fitted. I think once I get a new face for it, the incandescents will be replaced by LED equivalents. This is mostly just a hold-over because it was annoying me not being lit up.

More McIntosh

Finished up all the resistors on the boards.

power amp

Quite a lot of work involved, picking the best of the best for a good match.

what a mess

Redid the transistors on the boards also because they were a mix-n-match. Not matched, but all from the same batch and things are better. Got a capacitor list in and also the parts needed to make a transistor matching network.

boards

Seems to have been worthwhile. Hooked it up in the living room.

hookup

It really does sound like a decent amplifier (which it is). Now I’m torn- I kinda like having the quad in here!

McIntosh review

Took a bit of a while to get everything apart but managed to undo the thing from the case. The unlocking mechanisms were all jammed up.

unboxed

It was last certified to be good in 1975.

tag

Inside, modular design, a bit rusty and dirty, missing the top shields, all the mounting screws missing.

top view

It’s been worked on a fair bit in the past. Someone rather talented with a soldering iron stuffed this NPN into the socket then threw solder at it from a few feet away.

npn preamp

Pulled all the boards out and started to wipe it down. Then took a picture.

dirty chrome

Little bit of surface rust, but overall in fairly nice shape.

shiny chrome

Helpfully, somebody has removed the base at some time in the past and not put it back on. It does slot back into the cabinet and stay put, mostly.

base

Brought it up gently on the Variac. No smoke, sparks or anything untoward.

variac

Pulled the front off. Unfortunately it got rained on and the front panel started to peel off. The bulbs have been replaced with the wrong type also.

bulbs

The fascia has a thin transfer sheet stuck to it. The water had gotten in under it and caused it to ripple and wrinkle up.

face

Attempted to squeegee the water out and get it to sit flat. It kinda worked.

squeegee

Brought it up with a pair of sacrificial speakers. Thought the preamp wasn’t working, turns out it needs to be jumpered into the main amp.

speakers

Cleaned the cabinet with oil soap, then carefully rubbed it down with 000 wire wool and re-oiled it.

tung

Started measuring resistors and began replacing ones that are out of spec (+- 10%), trying to get within 2% for the replacements.

phase shift and regulator board

Quite a busy workbench. Table. Whatever.

workshop

All but one of the resistors on this board (20V Voltage regulator and 180 degree phase shift) were bad.

new resistors

A number on the right hand preamp board were also bad.

preamp

Buttoned all back up again, looking mostly respectable. More to come.