MA 6100

[c_dk]

Toshiba 2SC2240 and 2SA970 were Mac's near universal replacement PNP and NPN TO92 devices back in the 80s. Of coarse Toshiba has been out of the semi business for over a decade. BDent has had genuine replacements in the past. Fairchild KSC1845 and KSA992 also have worked well.

Obviously not for the darlingtons and certain other locations like the sentry monitor and muting circuits.

You need to pay careful attention to the legs......EBC replaced by ECB but nowadays that is common to sort out.

 

[PhilA]

I have used those before to good effect. I think I may have some spare ones left over from doing my Pioneer. I shall check and see.

Thanks

Phil

 

[PhilA]

Did the last of the resistors on the power amplifier boards tonight, dug out my spare transistors and decided to change out the small silicon on one channel, pre- and power-amp.

Granted I really need to build a matching network and a big box of transistors, but the whooiip and frrsscchhTTTTT it would occasionally make were the deciding factor in switching things out.

It's made a marked difference in the sound, considerably for the better. The right channel sounds like a fairly cheap transistor radio, the left is now much clearer. Sat switching between STEREO and STEREO REV. tonight, noting the difference between the two channels. The darlington transistors on the heat sinks now run cooler also.

I'm beginning to like this set.

Phil

 

[PhilA]

I decided it's been behaving itself enough to be tried out a little more. I've got it hooked up to my Sansuis in the living room, listening to Deep Purple. Had it up at about half volume, it's not dissimilar aurally to the Pioneer I have in here (QX747, rebuilt) and not bad to listen to, even in this short period.

Even unfinished, it is a keeper. I'm just making a list on Mouser of bits I need that I didn't have in stock. Also going to build a transistor matching network (from here: http://www.musicfromouterspace.com/analogsynth_new/TRANSISTORMATCHER/TRANSISTORMATCHER.html) and fifty or so of each type PNP and NPN (KSA992 and KSC1845 that I've used here and like the way they behave) and get all the small silicon matched up.

Edit: $59 order in place for transistors and capacitors and such.

--Phil

 

[PhilA]

Had a poke about today now that a few bits and bobs have been changed out. Brought the amp up on 120VAC as per the manual, measured voltages. Everything within 5%, let alone the manual-spec 10% on the main power supply points. Not bad. Worst is the 105V rail at 101.3V.

Been reading through this segment of the forum. I do have to agree. The Pioneer that's sat below the 6100 in the picture above has been thoroughly gone through- there's a thread on it on here- and despite that, without having done the caps on the McIntosh, only some non-matched silicon and fully gone-through resistors it has a definite edge on the Pioneer, particularly on vocals. I was comparing Abbey Road earlier and although the Pioneer isn't a bad machine by any standards (Which I also enjoy listening to) I'm in a quandary. The 6100 might end up replacing it.... but then I need a tuner and a quad decoder and a second amp...


It's a slippery slope.

--Phil

 

[62caddy]

.
It's a slippery slope....

With McIntosh? Surely you jest.

 

[PhilA]

It would appear so.

Preamp boards have new (albeit straight off the reel) silicon.. which is an improvement for now.

Listening to some classic rock right now. One thing that's noticeable is in other rooms in the house, it sounds much more "alive" than the Pioneer. That is, hearing it from the living room (not a big house, this!).

Gonna see how we get along with it. Wife's currently singing along with some of her favorite tunes so it can't be all that bad.

--Phil

 

[PhilA]

Excuse the big Macy's bags full of oddments the wife ordered.. but I moved everything.

Note the distinct lack of the Pioneer.

Yeeeeeah, I've grown to like the McIntosh.

--Phil

 

[PhilA]

Here is where we started today.

The old foam surround had gone all crispy and had turned to dust. So much so I vacuumed it all off!

Pulled the sticky (not very sticky any more) backing off.

Nice new roll of self-adhesive foam.

All cut out to match the original shape.

The original bulbs have toasted the cardboard. These ones had stuck to it, one broke taking it out. I think I'll be ordering the LED kit for this.

All reassembled and lit up. Not perfect but it looks better than it did.

Waiting to hear back from Audio Classics to see if they have the missing sheet metal in stock. Progress is progress!

--Phil

 

[PhilA]

Ryan at Audio classics has been very good in keeping me up to date with his progress

I ordered all but the main filter capacitors (those'll have to wait, just those two is an extra $55 that I didn't want to spend at this very instant) and a collection of transistors and the stuff I need to build a Hfe matching rig for NPN and PNP transistors.

Hopefully that's going to all be in before the end of the week. I'm going to try re-stuff the multi-cap, I have a Dremel that I can slice the can open with and I measured up a bunch of the Nichicon "pencil" style long-n-thin caps to fit inside. It's gotta be going a bit soft by now because it gives a rapidly vanishing hum on power-up. The rest of the audio caps are Nichicon PW series. A fully matched set of silicon and a recap, with redone resistors. This amp should be good for a long time yet.

--Phil

 

[PhilA]

Capacitors arrived in, so I decided this morning to do the boards. Preamps first:

Then the regulator/phase-shift board.

Finally the power amp boards. After/before comparison...

...and completed.

Played a bit of Floyd, now onto Mahler. Sounding good.

--Phil

 

[PhilA]

Built transistor matching circuit. Need to scrounge an old computer PSU to run it.

Phil

 

[PhilA]

Power supply rebuilt, circuit calibrated.

Random pnp transistor measuring in at 0.677V.

The rest to do at the weekend.

Phil

 

[PhilA]

Got set up and started testing, but I need to wait until later in the evening as the house doesn't have enough thermal inertia to hold temperature steady with the aircon cycling during the day.

Plug in, stabilize, record. Long process!


--Phil

 

[Tim 700]

Wow, great work!

 

[silversport]

Nice work...

Bill

 

[PhilA]

Thanks. I'm trying with it.

Was in town yesterday so stopped in to the hardware store and bought a foot of copper grounding wire. Bent it into an appropriate shallow horseshoe shape for two short lengths. Now I have a free RCA cable and the "correct" pre-to-power amplifier jumpers fitted.

Phil

 

[PhilA]

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.

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

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

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.

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

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

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

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

 

[BilboBaggins]

Great thread! I'm enjoying it immensely.

You are clearly a talented man with no fear of digging in deep.

Good on you!

 

[Mrv8q]

Enjoying it as well. That is one lucky 6100, to have been found by just the right guy!