3M M64 Halftrack

Oh...you bastid! :D ;) ;) SO dying for a good 2-track deck! Congrats Cory, that's a really cool machine!

Yeah...sick, huh?

Its gonna need some work, and the reality is that in current condition it will not cal to spec on the playback side because the play head wrap angle is WAY out and its got a deep wear pattern in it and until I send it to John French I won't know if it can even be relapped, so $50 now is important because its going to take $100's to get this machine back to "right".

And who knows what else is not right on it yet. But it IS a cool machine.
 
For sure, but I've not known you to shy away from a good fixer-upper project ;) Just thinking about that Ampex machine crankin' tracks through that MCI 400 series (or the Soundtracs for that matter) and down to the 3M...nice, man! Veddy nice!

Here's to hoping the heads can be worked with!

The day you score a $50 JH-110 2-track or similar...just send it my way, man! :D ;)
 
Cory's link to the larger sized picture files piqued my curiosity to see what was in there, so I found the head-on shot and decided to do my own "digital restoration" for Cory to have something to work toward or just have a smile.



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Cheers! :)
 
ROTFLMAO!!!!

HAHAH!!! :D

Lookit that guys! Ghost fixed the meters and replaced the missing aluminum cap on the repro knob of channel 1...wait...are those Otto's M-23 meters?? He's gonna be PISSED!

And touced up that big scratch from the supply reel on the dress panel and the scratches on the transport front cover!!

And..Ghost, thank you SO much for cleaning up the busted laminate on the leading edge of the console side panels. Looks MUCH better! And for tying up the wires under the electronics.

Oooo! And the output select lamp lenses are repaired! Nice! I was wondering where I was going to get those...

You...are...amazing.

Nice of you to lower the transport into the console all the way too...I carelessly left it slightly raised for the picture.
 
ROTFLMAO!!!!

HAHAH!!! :D

Lookit that guys! Ghost fixed the meters and replaced the missing aluminum cap on the repro knob of channel 1...wait...are those Otto's M-23 meters?? He's gonna be PISSED!

And touced up that big scratch from the supply reel on the dress panel and the scratches on the transport front cover!!

And..Ghost, thank you SO much for cleaning up the busted laminate on the leading edge of the console side panels. Looks MUCH better! And for tying up the wires under the electronics.

Oooo! And the output select lamp lenses are repaired! Nice! I was wondering where I was going to get those...

You...are...amazing.

Nice of you to lower the transport into the console all the way too...I carelessly left it slightly raised for the picture.
Glad you enjoyed my little restoration project! :D

And yes, those are Otto's meters!

Cheers! :)
 
I think its interesting that there are absolutely NO tension arms or otherwise anything to deal with dynamic changes in the transport like when stopping, starting, entering fast-wind, etc., at least not that I can see. So how does that work? Doesn't that make those changes harder on the tape?

I'm glad to report that all of the pinch roller hardware is there as far as the mounting brackets, linkages, etc. I was concerned that since the rollers were missing that other parts might be missing as well not having a good knowledge of those mechanics on this machine. Just the rollers, roller spindles and mounting screws are missing.

Otto, I re-read your entire M-23 thread along with the related prequel thread and it was helpful.

So it seems that the M-23 and M-64 are indeed very close siblings. Am I correct that the electronics cards are the same between the two machines and that there are just minor differences in the electronics chassis? And that the main difference between the two transports would be the capstan drive mechanism?

Also, still confused on the reel table surface. When you mount a reel on a table of your M-23 is the reel flange closest to the machine in metal-to-metal contact with the reel table?
 
I don't think I've ever noticed problems due to tape stress from changing modes. There are dashpots that damp the actuation of the pinch rollers. The transitions between winding modes work well. You kinda have to see it in action to see how it works. The manual actually describes how the transport control electronics accomplishes each such transition in exquisite detail.

The M-64 is pretty much an M-23 with the rim drive flywheel and capstan motor swapped for a belt drive flywheel and capstan motor.

My transport originally had the NAB hub only type of reel tables, but I never located matching reel hubs. Eventually, I took the 1/4" spindle type of reel tables from a small format M-79 transport spare and put them on. Recently, I got the standard 1/4" spindle reel tables from an M-23 parts machine (and some nice Otari hubs!) and I use those now. That means the reel hubs match as the 8-track Otari has the same style of Otari hubs.

Anyway, yes, the plastic center part of the 6-hole precision tape reel hub is directly on the surface of the reel table. BTW, the primary tape path reference is the lower flange of the incoming tape guide guiding the tape into the loop. That (and the Isoloop) are all it takes to guide the tape and keep everything lined up within the NAB head margins and provide good tape pack, assuming the reversing idler is vertical and working properly. The outgoing guides are a few thousandths wider and do not guide the tape in play mode.

The guide surface is set at a fixed distance from the capstan machined surface that the headstack mounts on. The tape should touch but not bind on the incoming guide flanges. The manual says you don't need shims to adjust the guide surface. I took a bunch of shims from under the guides when setting up my machine and it finally worked right when I did that (and had a new idler).

Cheers,

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

All I can say is that 3M machines have a sound that can level cities. The earlier machines are a tad better than the M-79s, in terms of low phase shift at the high end. They are designed to drive 150 or 600 ohm loads and eat +4 nominal signals for lunch. To monitor the M-23, I unbalance the outputs at the patchbay and then run the signals through -10 dB pads before running back to the mixers returns to avoid overloading the return inputs. Even then it doesn't seem to require makeup gain to have a reasonable signal.

Cheers,

Otto
 
All I can say is that 3M machines have a sound that can level cities. The earlier machines are a tad better than the M-79s, in terms of low phase shift at the high end. They are designed to drive 150 or 600 ohm loads and eat +4 nominal signals for lunch. To monitor the M-23, I unbalance the outputs at the patchbay and then run the signals through -10 dB pads before running back to the mixers returns to avoid overloading the return inputs. Even then it doesn't seem to require makeup gain to have a reasonable signal.

Oh I'm not questioning whether or not they sound good, I just find it interesting because power supply voltage is directly related to headroom in audio electronics, and 30V peak-to-peak differential is pretty much the standard for decades now (15V bipolar supply) but when you go back a bit earlier it seems that higher supply rails were the norm in pro gear...Ampex with 39V unipolar, my MCI console with 24V bipolar (48V peak-to-peak)...The printing on the M-64 electronics power supply module transformer indicates 28V RMS on the output side so there you go, as far as the unregulated power. Really anxious to track down a manual for this thing.

Hey, I took some video of the M-64:

YouTube

The main problems for sure at this time are dodgey transport controls and non-functional optical sensor circuitry.

My first suspect with the transport controls would be this relay hanging down underneath the transport:

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The coil terminals of that relay on terminals 13 and 14 (standard "ice cube" relay) go across the PLAY control. Its not factory as far as I can tell.
 
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Cory, loved watching this vid! That's a cool machine and I enjoyed seeing it in some kind of action! Love the sounds, love the transport movements, love those big ol' buttons :D

I suspect that a good sweetbeats-quality cleaning-up alone will do wonders for this machine. A lot of it just looks tired and gummed up, but you're brilliant at dealing with that kind of thing!

I can't really comment on the machine's functionality, never used one, but the reel idle tension takeup thing reminds me of our MCI machine, you'll recall that vid I posted where I was adjusting the reel idles. Also the CAL setting on the electronics--on MCI, switching to CAL takes the trim pot out of the equation and instead selects a fixed level for calibration.
 
You're right about the channel power supplies being "cute". Everything about the machine's design is symmetrical, centered, and........ cute.

Except for the parts that are missing and non-functional of course :)
 
You're right about the channel power supplies being "cute". Everything about the machine's design is symmetrical, centered, and........ cute.

Except for the parts that are missing and non-functional of course :)

But they'll be cute too when I find them. :)
 
Cory, loved watching this vid! That's a cool machine and I enjoyed seeing it in some kind of action! Love the sounds, love the transport movements, love those big ol' buttons :D

I suspect that a good sweetbeats-quality cleaning-up alone will do wonders for this machine. A lot of it just looks tired and gummed up, but you're brilliant at dealing with that kind of thing!

I can't really comment on the machine's functionality, never used one, but the reel idle tension takeup thing reminds me of our MCI machine, you'll recall that vid I posted where I was adjusting the reel idles. Also the CAL setting on the electronics--on MCI, switching to CAL takes the trim pot out of the equation and instead selects a fixed level for calibration.

Yes I recall seeing the same reel table activity on that vid of your MCI machine. On the 3M that's a sign that the optical sensor isn't working because it should only do that (go into a tension hold mode) with tape loaded, but since the sensor is shot it thinks tape is loaded all the time. I tested it by shining a flashlight at the sensor and it didn't curb the behavior so there will be some work to do there.

And yes on the CAL setting, that's what I'm shooting for/hoping for. My Tascam BR-20T has the same thing, and the level pots on the Ampex 440C are push/pull and do the same thing in one of the positions. Nice feature. I'm assuming it is the same with the M-64 electronics.

Yeahhhh...I'm on the fence about this machine...no need to make and quick decisions, but I get shoved around on the fence when I watch the video and hear the sounds.

More updated info in the next post....
 
So I'm doing well at answering some of my own questions...

Brakes: I rhetorically asked the question in my video regarding the lack of brakes that I could see. Answer --- there aren't any. Yup. No brakes. The reel motors handle dynamic braking, one or the other depending on the direction the tape is traveling. How do you like that? No need to adjust the brakes.

Amplifier electronics power supply voltage: each electronics module is indeed powered by a dedicated +28VDC unipolar regulated supply. This is surprising to me because that is an even smaller peak-to-peak voltage than the run-of-the-mill 15VDC bipolar supplies so common in audio equipment. Supply voltage is directly linked to headroom, and the typical 15VDC bipolar powered device has an internal operating level of -10dBv for this reason. My Ampex stuff is +39VDC unipolar powered, which is greater than 18VDC bipolar supplies...my Soundtracs MX mixer audio runs on 17VDC bipolar rails...my MCI JH-416 console runs on 24VDC bipolar rails, so it is quizical to me that the 3M audio electronics run on the equivalent of 14VDC bipolar rails. I'll have to look at the schematic some and see if I can see something that differs in the amp electronics to other designs.

BTW, I found a full service manual in pdf for the "M-500" 3M tape machines (that would be the 1" and 2" versions of the M-56). The transport is VERY similar to the M-64, and I believe the M-56 uses the same audio cards as the M-64 so the schematics should help...better than nothing. May not match totally since the cards are in drawers in the M-56 rather than in separate modules so wiring diagrams won't match, etc., but the circuit topography should be very similar if not the same.

I confirmed with Terry Witt that he doesn't work on the contoured 3M Isoloop pinch rollers. Contoured? Let me explain for those of you, like me, that had no idea how the "Isoloop" tape path maintains constant tape tension in the "loop" (the section of tape between the incoming pinch roller and the outgoing pinch roller). Look at this diagram from the M-56 manual and keep in mind that the M-64 rollers and capstan are shorter, but this will work for the purpose of explaining:

Isoloop%20Tape%20Drive.jpg


Because of the contoured grooves on the rollers and on the capstan shaft the diameter of the driving surface is smaller on the intake side of the loop as compared to the output side...the pinch rollers are (obviously) not the same part between the two sides. Does that make sense when looking at the diagram? So because the diameter of the driving surface on the output side is greater, it wants to pull a greater amount of tape per revolution of the capstan than the intake side...that creates tension, and it is constant because the driving surface diameters are constant and the rotational speed of the capstan is constant. This is a brilliant non-servo constant tension system. I love it the same way that I like mechanical fuel injection systems. Then the holdback and takeup tensions provided by the reel motors simply control tension between the supply reel to the intake pinch roller, and then from the output pinch roller to the takeup reel. Tape tension management in that loop is isolated from the rest of the tape path...an isolated loop or "Isoloop". Now...just how gentle is this on the tape? Good question. There is internet "lore" about the "3M tape stretchers". I've gotten the impression from at least on member here that that is bunk...I've gotten the opinion from another individual whom I also respect that it was a real issue, so I don't know. I can tell you that it makes the condition and quality of the pinch rollers CRITICAL...can you see why? And I betcha that's why Terry Witt won't work on them. And the capstan motor has to have quite a bit of torque potential on the capstan shaft with the size of that flywheel and the relatively tiny diameter of the motor pulley. At some point I oughta try and figger out how fast the capstan motor is humming when the transport is set to 30ips...look at the motor pulley and the flywheel size differences in this image from the M-56 manual:

Transport%20Bottom%20View.jpg



Regardless, cool stuff.

Here is a closeup shot of the capstan shaft...you can see the different diameter surfaces between the light and dark bands at the bottom of the shaft. Subtle.

Capstan%20Detail.jpg
 
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Yes I recall seeing the same reel table activity on that vid of your MCI machine. On the 3M that's a sign that the optical sensor isn't working because it should only do that (go into a tension hold mode) with tape loaded, but since the sensor is shot it thinks tape is loaded all the time. I tested it by shining a flashlight at the sensor and it didn't curb the behavior so there will be some work to do there.

I scared myself the first time I accidentally shined a flashlight on the sensor while tape was threaded and the unit was powered up. I hadn't installed a working sensor bulb or tried to get that circuit working. So, I had the tape moving and it shut off when the flashlight beam hit the sensor while I was working on some small transport adjustment. Scared the c#@p out of me. Of course, then I knew the circuit was working and I just needed to get new bulbs to get that thing working.

BTW, I watched the video. Not sure, but I think the capstan motor is quieter than mine. Mine's pretty noisy.

Also, I think I posted the functions of the cards earlier in this thread. M-56 cards are the same as M-23, but M-64/M-56 machines are belt drive and seem to be mostly 15/30, while more M-23s seem to be 7.5/15.

Keep up the good work!

Cheers,

Otto
 
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Been many moons since I updated this thread.

I'm no longer on the fence about this machine. Did some tradsies with a friend. Letting go of a pile of Ampex stuff including my 440C halftrack project for a fully functional 3M halftrack with 3 electronics modules. VGC. Not sure yet if it is an M-23 converted to belt drive or whether it is actually an M-64. Several things point to it being an M-64 which is sweet. That means my current machine would become a parts machine and the one that's coming would be the primary machine. The nice thing is that the one that's coming is rack-mount configuration rather than console mount which is nice because the console-mount versions are quite a bit wider and space is an issue for me. The other nice thing is that the 3 electronics modules that come with it actually have the meters intact which I am lacking.

The story on this machine is that it was in a church installation since it left the factory until several years ago when it was decomissioned and purchased by my friend. The funny thing though is that the original owners would only sell one of the two electronics modules with it. My friend subsequently picked up a pair of M-23 modules and that makes the three that are coming with it. When my friend got it he sent it to John French to look at the heads. This machine has Saki heads on it but the repro head was (IIRC) worn unevenly and couldn't be lapped so John had a near-new Otari repro head which he installed and then setup the block. So its ready to go as far as that's concerned. Its straight-forward otherwise and looks to be very clean and straight.

3M_Front_2_1_1.jpg


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Oh and to answer a question from earlier about the audio power supply being only 28 volts...the main transformer in each electronics supply is labeled 28VAC, but that's RMS. I think the regulated DC rail is about 36VDC. Not the same headroom potential as an Ampex 39V supply but equivalent to the swing on an 18V dual supply so that's good. And, again, the I/O transformers are just...huge. This thing *should* have quite a sonic signature to it.

Considering all the trouble I'm having with the machine that is supposed to be my halftrack machine (my Tascam BR-20T), this may actually be a very good thing that a functioning relay-logic discrete machine is coming (remember, IC's and I don't really get along that well when it comes to fixing and troubleshooting...them little buggers intimidate me).
 
No console, which is actually a good thing because if it WAS a console-mount, then the transport face and electronics faceplates would be wider and not rack-mountable, and I'll benefit greatly from the flexibility of being able to rack mount them.

With the electronics assemblies its not a big deal because they are easy to convert to rack-mount...not so with the transport. That would involve cutting metal.

These machines came from the factory either mounted in the factory console (see the pics of my original machine at the top of the thread), or naked like this new one for rack mounting, and i suppose you could put them in road cases too but i don't believe 3M had factory cases available for these machine unlike Ampex for many of their period machines.
 
HAHAHA!! That's sweet, Jeff! Heheh! :D

Say...can you get me the other "3M" logo meter you got for the photo shoot? Heeheee. :)
 
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