My vintage McIntosh MX-110 preamp surprised me today. Follow up post #61!

Sweet. And/Or maybe someone else can post a pic of the schematic, or the preamp innards themselves. I love looking at that kind of stuff.

ccm

 

This is an interesting idea. But, I bet if you duplicated the circuit using modern parts it would sound completely different. May as well just find a nice MX-110. They are a bargain in the world of vintage McIntosh gear.

I'll see if I can find some inside pictures that I took when recapping my MX-110 a few years ago.

I wonder if some of the magic is coming from the 6D10 Compactron? If I recall correctly, the 6D10 is utilized in the tape loop circuit. Pretty sure also that the
6D10 is only used in the "Z" series MX-110.

 

Your Marantz biased...lol

 

Do people prefer the MX110Z with the brushed aluminum lower front-plate or the shiny gold look? I have a brushed version now, but miss the shinier look of my old one.

 

Yeah, I suppose you're right Steve, I traded my last one towards a more modern preamp, which did not appreciate in value like the Mac has

 

Very cool. Watching this space.

ccm

 

From this picture I pulled off the 'net, I can't really tell to what extent the tape loop runs through the circuit.

 

Steve, how about tube rolling to locate the extent of the tape loop circuitry? You could roll one set of tubes at a time until the sound changes through your tape loop. That would localize the TL circuit.

 

I found a schematic of the M series; though it's hard to read, it appears the tape loop goes through the single 12AX7. If your Z has the same loop/12AX7 layout, maybe try that one first?

 

^Good idea, T+V.

A look at the schematic in combination with the above will help us see if anything else in the circuit is involved.

It may be easier to read the schematic if we know which tube position to focus on.

Or, the schematic might be totally obvious on its own.

Man, what I wouldn't give for a good 3 months off to dig into a hot-rodding project on something like this.

The contracting biz is like that, though. I'll get it before a few years are out.

I am loving this thread.

ccm

 

Paper or electronic? Can you post it?

ccm

 

Here is a service manual for a regular MX-110. Each channel uses 1/3 of the 6D10 as a buffer.
http://www.pmillett.com/file_downloads/McIntosh/MX110_service_manual.pdf

 

I found my Z series schematic. It looks like with the tape monitor "in", the signal bypasses the 6D10. Each channel goes through 1/2 of 12AX7 (V15) and then through both sections of a 6U8 (V16 for the left and V17 for right). So, one pass through a 12AX7 and two passes through a 6U8.

The owner's manual refers to this 12AX7 as the "left and right 2nd audio amplifier" and the two 6U8's as the "left 3rd audio amplifier" and "right 3rd audio amplifier. "

Hope that makes sense! (and hopefully I'm reading the schematic correctly!)

 

What you are saying is correct but used as described in post 61 the 6D10 cathode follower is the only active stage in the circuit.

As you say one could bypass the 6D10 by hooking a component to the tape monitor inputs and using the main outputs. This would leave the whole line stage in the circuit.

 

Dale is correct. I read post 61 again and studied the schematic again. The AUX input goes to the 1st audio amp in the 6D10. Then to the tape right or left output. Further amplification and tone controls are bypassed.

The magic is in a Compactron?!

 

The 6D10 is also one of the key tubes in a Fender Super Champ, which is one sweet sounding little amp.

I know the distortion in a guitar amp is not what we're going for here, just wanted to state where I've seen the 6D10 before.

IIRC, wasn't the RCA 6D10 the one to have? Steve, what brand is yours?

It would seem that a much simpler version of this preamp could be knocked together by a talented hobbyist, without the phono stage, tuner, tone controls, and switches for all of those channel summing features.

Find the vintage transformers, unclutter the layout, dress the wiring for the least interference. Add in the latest and greatest in component technology with some good shielding, and the results could be very cool.

ccm

 

I think all 6D10's were made by the same manufacturer, so it doesn't really make any difference to roll this tube.

 

Does anyone run your MX110 with or without wood case? Heat, tube life, etc.,

 

Well, here are at least two different configurations.

Side getter:


O getter:


ccm

 

Also, in the 6U8 position, this strikes me as a tube that I would have to try:

http://www.ebay.com/itm/ECF802-SIEM...3?pt=Röhren&hash=item43a46a67cb#ht_676wt_1037

Probably the same thing in Tele version:
http://www.ebay.com/itm/10-x-ECF802...ren_Valves&hash=item564a953d66#ht_1441wt_1270

I know you said a while ago that the Tele ECF82 was muddy sounding to you, Steve, but it looks as though these are the no holds barred model, just like the tele ECC803's are to the ECC83's.

The 802's aren't the same animal, and might be worth a shot, since the "80" series is the uberbeast line.

For anyone who wants to get more deeply involved in this thread:

http://www.ebay.com/itm/26104765680...AX:IT&_trksid=p3984.m1438.l2649#ht_500wt_1287

I did the hunting for y'all. I'm WAY too many projects behind to take this one on, as delightful as it would be.

ccm

 

I believe GE was the only manufacturer of Compactron types in the US, but am not sure. I think someone in Europe made a few of the sweep tubes later on.