3M M64 Halftrack

sweetbeats

Reel deep thoughts...
Who knows what about these things?

I'm giving a helping hand to an acquaintance who got ahold of one at an auction. I'm gathering info to help him sell it.

What I know in general:

  • The M64 was the 1, 2, 4-track version of the M56.
  • Late 60's/early 70's
  • All discrete solid-state electronics

What I know about the one he's got:

  • Console is in solid shape but the laminate has been stripped off of most of it so it looks bad.
  • It appears to be all there except the meters have been damaged and one reel table has the wrong hardware so it isn't fastened to the motor hub properly. There may be a little trimwork missing. The upper left guide cover is present but the pins are missing to affix it to the top of the guides.
  • It powers up and I can confirm that the reel motors work but the transport behavior can't be tested because the lamp(s) in the optical sensor are out, but the reel motors spin strong and fast.
  • Heads look pretty good though the wrap is wrong on the record head (the gap is not centered) and the zenith is off on the repro head (a little keystoning) but it looks like there is a lot of material for a relap.
Its a beast.

There are no tension arms on this thing...and...and...no pinch roller. The have a pretty advanced (for the time) tension control via the reel motors, yes?

Here are some select pics below. Full size versions as well as the complete collection of 44 pics are here: Index of /3M_M64

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Fill me in!
 
I have a copy of Tremain's Audio Cyclopedia, and it has a small section describing these machines and the unique way they record. Let me look it up...
 
What is that device in the drawer? I thought it was a motor at first. Is that some horrible large electrolytic? And if so, does it still work?
 
I found the section about it in the book... it's several pages worth of info; I'll scan them or something so you can check it out, there's no way I'm going to type it all.
Judging by the book, there was a pinch roller, but it appears to be missing on the one in your pics? Hard to tell for sure...
 
What is that device in the drawer? I thought it was a motor at first. Is that some horrible large electrolytic? And if so, does it still work?

That's the local power supply for the electronics module...yes that's an electrolytic cap...the primary filter cap.

I would be surprised if it DIDN'T work. Every professional unit I've worked with from that era (Ampex stuff primarily) has power supplies with those huge caps and even 40 years later they run clean as you'd want. The supplies were very well designed and the caps were of very high quality.

Here's the main filter cap for the 24V transport power supply in my 1969 Ampex...this is a new one but the same size as stock...It didn't need to be replaced...just being over-cautious:

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I found the section about it in the book... it's several pages worth of info; I'll scan them or something so you can check it out, there's no way I'm going to type it all.
Judging by the book, there was a pinch roller, but it appears to be missing on the one in your pics? Hard to tell for sure...

That would be fantastic if you were able to scan the info into a pdf...thank you so much!
 
That's the local power supply for the electronics module...yes that's an electrolytic cap...the primary filter cap.
I would be surprised if it DIDN'T work. Every professional unit I've worked with from that era (Ampex stuff primarily) has power supplies with those huge caps and even 40 years later they run clean as you'd want. The supplies were very well designed and the caps were of very high quality.

Right. The only professional deck I've seen in person is my A807 and the PSU caps are only about a half or a third of that size. I was wondering what would happen if the 3M one blew up. Probably take the house down. :P
 
Never had the unfortunate pleasure to be around when something like that goes, but I understand that it is quite an event. I will say that when I smoke tested the PSU in which that huge Mallory cap is installed I put on ear protection, flipped the supply over so the top of the can was facing the floor and placed a large piece of heavy-guage metal shrouding over the rest of it so it was boxed in by steel. This was after checking, re-checking and checking some more to make sure all my connections were correct. I've come to know I should never underestimate my ability to be a complete ignoramous.
 
I know a fair amount. M-64 is similar to M-23, except that it has belt-drive instead of rim drive. This is a two-channel NAB unit, probably 30/15. No sync cards (#9 slot), typical of a mix deck. Original Mincom heads with a fair amount of wear. There should be a slide on shield for the play head, but I don't see it. Sorry the meters are trashed. The tape is actually capstan-driven and there should be two different, differential pinch rollers for the Isoloop, an incoming roller on the left (clearly missing) and an outgoing one on the right (can't see from the pix). They both swing in to press on the capstan when in play mode. The lamps are a standard bulb. Need to check the number, 387 is what comes to mind, but that might be the one for the transport buttons, which is a different style. They are both like $3 for a box of 10 at 1000bulbs.com.

Hope that helps,

Otto
 
I was hoping you'd chime in, Otto...thanks.

I'll have to look at some pics of the M-23 to see what's missing with the idlers...hardly any M-64 pics to be found...I suppose M-56 pics would work too.

The head shield is there...it was just off for the pics.

Thanks! ;)
 
I was hoping you'd chime in, Otto...thanks.

I'll have to look at some pics of the M-23 to see what's missing with the idlers...hardly any M-64 pics to be found...I suppose M-56 pics would work too.

The head shield is there...it was just off for the pics.

Thanks! ;)

I think I had it backwards. The 387 bulb is for the transport button illumination. The tape runout sensor light bulbs are 313 or 1820. The 1820's are preferred as they are only 15 cents each and have a nominal life of 1000 hours, versus 500 hours for the 313s, which are 30 cents each.

In North America, I'd recommend Matt "Buster" Allen of Allen Sound in Nashville as the first contact for 3M Mincom specific parts. In the EU, the contact is Sir Clive Kavan. A great many of the parts in the machine are standard parts available from standard sources.

BTW, I have a complete operation and maintenance manual for the M-23. At some point, I'll probably scan it and send the file to Matt so he can make it available. I have the very rare extra section on Dynatrack, but I do not have the parts list appendix. Dale Manquen does have the parts list. Matt may also... I haven't needed to ask.

Also, if the project starts to look like more than the owner is really up for, let me know, as I could probably make some good use of the machine.

Cheers,

Otto
 
Also, in case it isn't obvious, the cards are as follows:

1) bias/erase
3N) NAB erase coupler (doesn't do much, but that is where you would put a 3D card for Dynatrack machines)
4) record
5) is the center meter module
6) line amp
7) playback. a "7/9" card can go in either the 7 or 9 slot. Mix decks only have cards in the 7 slot. A multitrack machine should have one in both slots on every channel because number 9 is ...
9) sync playback

Cheers,

Otto
 
Thanks for all the info, Otto...I'd run across the Allen Sound website...good stuff.

Also, if the project starts to look like more than the owner is really up for, let me know, as I could probably make some good use of the machine.

To be clear, neither the owner nor I are interested in refurbing the machine. I'm simply assisting in gathering information to help him list it. He wants to sell it.
 
For $50 its hard to pass up...the transport is pretty slick...SUPER thick beefy cast webbing on the deck plate...I hesitate to make comparisons but the transport is more refined than an Ampex 440 and more substantial, yet the electronics are in the same vein (i.e. ballsy discrete class A).

Questions...Otto is probably going to be the one to reply...

  1. What kind of supply powers the amps? Unipolar? Bipolar? What voltage?
  2. Am I correct that the transport cannot be rack mounted? That it is designed to sit in the console?
  3. Is there a cork or rubber pad that goes on the reel tables?
Gotta find a manual, pinch rollers and associated hardware, and some meters.
 
For $50 its hard to pass up...the transport is pretty slick...SUPER thick beefy cast webbing on the deck plate...I hesitate to make comparisons but the transport is more refined than an Ampex 440 and more substantial, yet the electronics are in the same vein (i.e. ballsy discrete class A).

Questions...Otto is probably going to be the one to reply...

  1. What kind of supply powers the amps? Unipolar? Bipolar? What voltage?
  2. Am I correct that the transport cannot be rack mounted? That it is designed to sit in the console?
  3. Is there a cork or rubber pad that goes on the reel tables?
Gotta find a manual, pinch rollers and associated hardware, and some meters.

Not where I can get to the manual. IIRC, supply to the channel electronics is unipolar +28 V, but I'll have to verify that when I can look at the manual.

They made rack mount transports. In fact, mine is just such a transport, though I built a minimalist console for it. The console transports have a different, wider, top panel and there are extensions on the sides of the deck plate so that it mounts in the larger space. You could probably modify a console transport to work within rack mount spacing, since the guts of the transport are the same. Might have to do some fairly extensive mods on the locations of transport controls to fit within that space.

I've never needed or used cork pads on the reel tables. The reel table height can be adjusted by pulling the top panel, loosening the set screw on the lower nut attaching the reel table to the reel motor spindle.

I always run tape on the M-23 using six hole precision reels on both reel tables and the alignment is pretty much right on.

I'll get back to you about the PSU voltage when I can. Looking a few posts up, it seems my recollection on the bulb type numbers was correct.

Cheers,

Otto
 
So the reel tables are just metal surface and the reel adapters mount straight to that?

Wow...+28V unipolar sounds...low. That would be equivalent to a 14V bipolar supply.
 
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