3M M-23 mix deck...

[ofajen]

I thought I'd start a new thread in case we have more discussion on the M-23, since the previous thread started out as an info item on the labeling of tape channels and the tracks they correspond to on the tape.

I'm a bit concerned about the idler. I took it off and tested it and it has a fair amount of wobble. It may be repairable, but I'm not sure. I was able to get the machine working a bit better by rotating the idler base to the most favorable angle, but that wobble may produce a flutter issue and may also affect the bearing lifetime, so it's better to fix or replace, I think.

This is one of those times when I will seek counsel from Dale Manquen, a former 3M employee, who is a real expert on these machines. I hope the idler can be repaired. Otherwise, I'll need to contact Matt Allen, since he is the keeper of the main store of NOS 3M parts.

Cheers,

Otto

 

[sweetbeats]

Just for reference, everybody, the origin of this thread is in this thread here.

Otto, does the idler use ball or roller bearing cartridges, or is it a bushing?

I've (happily) found that almost all the roller bearings on my Ampex 440 are are very common standard size (608Z type) so I was able to source off-the-shelf generic parts. Only the Capstan motor uses a different size. The rotary guide, reel idler and reel motors all use the 608. Wondering if 3M, being US-based may have employed the same ideology...

 

[ofajen]

Just for reference, everybody, the origin of this thread is in this thread here.

Otto, does the idler use ball or roller bearing cartridges, or is it a bushing?

I've (happily) found that almost all the roller bearings on my Ampex 440 are are very common standard size (608Z type) so I was able to source off-the-shelf generic parts. Only the Capstan motor uses a different size. The rotary guide, reel idler and reel motors all use the 608. Wondering if 3M, being US-based may have employed the same ideology...

The reversing idler has two identical bearings, top and bottom. NMB is the make and SSR-4ZZ is the code. I should probably get some more, but my real problem is that the shaft of the idler base is slightly bent, meaning that the idler is not properly vertical and it wobbles.

Otto

 

[sweetbeats]

Can you tell if there was a definite point of the bend? Think you can straighten it? I had good luck straightening the reel motor shafts on my Ampex 440...they had bent just past the bearing so I was able to use a deep drive socket and a socket extension and a dial indicator to get them back pretty close to straight (<0.0005" off)...I guess I'd have to see what the part looks like, but I bet it can be fixed.

 

[ofajen]

Can you tell if there was a definite point of the bend? Think you can straighten it? I had good luck straightening the reel motor shafts on my Ampex 440...they had bent just past the bearing so I was able to use a deep drive socket and a socket extension and a dial indicator to get them back pretty close to straight (<0.0005" off)...I guess I'd have to see what the part looks like, but I bet it can be fixed.

Base is a cylinder, about 5/8" tall and 1" in diameter. Shaft is 1/4" diameter and 1" tall. I think the bend is pretty much where the shaft meets the base. No harm in trying to fix it. It will cost me $125 plus shipping to buy a whole new reversing idler unit, which would be a waste if I can fix it.

Cheers,

Otto

 

[ofajen]

Can you tell if there was a definite point of the bend? Think you can straighten it? I had good luck straightening the reel motor shafts on my Ampex 440...they had bent just past the bearing so I was able to use a deep drive socket and a socket extension and a dial indicator to get them back pretty close to straight (<0.0005" off)...I guess I'd have to see what the part looks like, but I bet it can be fixed.

I don't have a dial indicator. Looks like a tool that will be handy from time to time. Any recommendation on one that will do this job and is reasonably priced?

Cheers,

Otto

 

[sweetbeats]

Either one of these will do just fine...I think mine is the same as the white-faced version. Not Starrett quality, but not Starrett price either and get's the job done just fine. I've been really impressed with mine for the price. Then you can get a magnetic base like this or this.

The trick is that you'll have to unmount the idler base/shaft assembly and somehow mount it in a drill press or something in which it can rotate so you can put the dial indicator probe on the tip of the shaft and measure the runout...find the high point, bend, check, find the high point, bend, check and so on. Maybe you've already got that figured out but if not maybe I can help if you can put up a picture of the base/shaft assembly and describe how it mounts to the transport plate.

Gotta get that bad boy to treat yer tape right!

 

[ofajen]

I'm going to take the base to a local machinist and see if he can bend it back, or perhaps make a new part cheaper than I can replace the whole assembly. By the way, do you have a good source for bearings? I'm looking for SSR-4ZZ bearing assemblies. One got slightly dinged while I was tinkering with it and should probably be replaced.

Cheers,

Otto

Either one of these will do just fine...I think mine is the same as the white-faced version. Not Starrett quality, but not Starrett price either and get's the job done just fine. I've been really impressed with mine for the price. Then you can get a magnetic base like this or this.

The trick is that you'll have to unmount the idler base/shaft assembly and somehow mount it in a drill press or something in which it can rotate so you can put the dial indicator probe on the tip of the shaft and measure the runout...find the high point, bend, check, find the high point, bend, check and so on. Maybe you've already got that figured out but if not maybe I can help if you can put up a picture of the base/shaft assembly and describe how it mounts to the transport plate.

Gotta get that bad boy to treat yer tape right!

 

[sweetbeats]

Good call on the machine shop, though that may not be cheap. Having a new part machined is the ultimate tho'.

The SSR-4ZZ may also be found as R-4ZZ ('R' for roller I think) or SR-4ZZ (the 'S' there is stainless). It is 0.250" ID, 0.625" OD, and 0.196" thickness.

I got bearings for my Ampex 440 at vxb.com. Limited experience with them but what I ordered seems to be of good quality and there were no hassles with the order.

Do a Google search for other bearing suppliers. Take note of the "ABEC" rating on a particular bearing...if there is no ABEC rating then assume it is ABEC-1. The higher the number the higher the precision and finish of the bearing (i.e. smoother). You generally won't find anything over ABEC-7. In fact at vxb on their 0.250" ID page I didn't see anything over ABEC-1. No big deal but considering the reversing idler is smack in the middle of the tape path it couldn't hurt to get something as smooth as you can find for a price you are willing to pay.

Otherwise, looks like vxb has R-4ZZ and SR-4ZZ offerings.

 

[ofajen]

Otherwise, looks like vxb has R-4ZZ and SR-4ZZ offerings.

They have that bearing with ABEC rating of 7 for $30. I decided to go ahead and buy a replacement assembly for $100. I'll keep the good bearing in the old one as a spare.

The Eiko bulbs came today and now the tape runout lamp and sensor system work perfectly! First time I ever tried to get that thing running on one of these machines. Now I don't have to turn it off to change tape reels!

Should have the transport reassembled within a week. With any luck, I will be able to get it at least close to spec. Down the road, it will probably make sense to recap the audio cards, PSU and transport logic card. I'm in no hurry, however, unless the audio cards won't let me get it up to spec.

In the mean time, I'm plotting a replacement for my M-56 8-track, but one that is a bit smaller and quieter. At this point, I'm thinking it may be a Stephens 16-track, which will actually fit exactly in the little console I just made for the M-23 and will be much quieter than the M-56 (no capstan motor).

Cheers,

Otto

 

[sweetbeats]

I think that is pretty sweet that you were able to source a new part. Likely cheaper than the machine shop route and genuine to boot!

We want more!!!

 

[ofajen]

I think that is pretty sweet that you were able to source a new part. Likely cheaper than the machine shop route and genuine to boot!

We want more!!!

The 3M world is small, but somewhat connected. We all know that Bart Gass, a long-time 3M field rep, got hold of a big bunch of parts when 3M quit the biz, and we know that Otho Wilburn bought that stuff from him about 10 years ago.

I mentioned here, a year or two ago, the saga of how my Auditronics console, a bunch of Mitch's gear, including the M-23 he's now willing to let me grab, the 3M parts store from Bart and who knows what else, went missing when Otho disappeared from view for many years.

A young guy named Matt Allen got interested in 3M machines a few years back and we chatted about various stuff, and I kinda brought him up to speed on the various machines and this whole saga came up.

By what looks more like divine intervention than coincidence, Matt ended up graduating from college and heading to Nashville, where, among other things, he now works some for Randy Blevins.

One day, Randy sent Matt to check out a warehouse for stuff they could buy and resell. Turned out most of our stuff was there, and Matt happened to know the story and happened to know what Otho had "accumulated" from Mitch and me, and told the warehouse owner. That guy had basically been paying Otho's considerable storage facility charges for the last ten years and, despairing that Otho would ever be able to repay, was now just trying to sell off the stuff (which he presumed was Otho's) to recoup his storage fee costs. However, when Matt told him that much of the stuff belonged to Mitch and me, he was honest enough to give all that stuff back, and that was also when Matt came into possession of the big 3M parts store, which Otho had stashed in that warehouse.

A long way of saying that Matt, while not a technical expert on repairing the machines, is now the first person to ask when looking for 3M parts, and in most cases he has what we need. That makes things easier than you might otherwise expect them to be.

Cheers,

Otto

 

[ofajen]

Down the road, it will probably make sense to recap the audio cards, PSU and transport logic card. I'm in no hurry, however, unless the audio cards won't let me get it up to spec.

Turns out I have some original "Beaver" brand electrolytics on the #1 erase/bias cards and the #6 line amp cards. Those old things have to go. I've ordered new caps from Mouser.

Cheers,

Otto

 

[sweetbeats]

Otto,

Thanks for the background story on the parts...that is verrry interesting.

I've heard of those Beaver caps...I've heard they were not good from the start. Bye-bye Beaver...

 

[ofajen]

Otto,

Thanks for the background story on the parts...that is verrry interesting.

Yeah, it wasn't that huge for me, just a little Auditronics console that Otho wanted to buy from me but then never bothered to pay up pursuant to our agreement. It needed some TLC, and once it resurfaced, I ended up selling it for about $600 to a young guy who had the time and wanted a high-end sounding small console. The PSU had disappeared, unfortunately, so he had to get/make a new one.

Mitch, OTOH, had, I think, two 24-track Lyrecs, the M-23 and some other stuff that disappeared for all those years. He was glad to get the stuff back. Too bad the M-23 seems to have some corrosion on the chrome parts.

Cheers,

Otto

 

[ofajen]

I've heard of those Beaver caps...I've heard they were not good from the start. Bye-bye Beaver...

Yeah. Perversely, I was glad to see those caps in there. I had some concerns about the overall performance of the audio cards, though the idler issues were the big problem. Still, having ancient caps in key positions on the line amp cards gives me hope that tidying up the basic audio performance of the cards might only involve replacing half a dozen or so caps. Most of the other, small caps don't look nearly so old. Or maybe they just age more gracefully.

Cheers,

Otto

 

[ofajen]

I replaced the old Beaver caps with new Xicons. Mainly on the #6 line driver card. Now the system does a bit better on the input side. Monitoring a test tone, the output level is flat to 20K, though the VU meter reads about half a dB low at that point. It's still a bit off spec on the low end, with both output level and VU showing -1.5 db at 30 Hz. I'm still trying to determine what's causing that. May not be a problem at all. We'll just see how overall response looks once my new idler shows up.

I was having trouble with the output level on one channel being low relative to the meter reading. Then I noticed it was exactly 6 dB too low. The output impedance setting was 150 ohms, not 600 ohms. Doh! Now it's set where it should be and the levels all match.

Cheers,

Otto

 

[ofajen]

I painted some shelves yesterday. While I was at it, I painted the consoles for the M-23 and A3440S. Here are some pictures of the M-23. I really like this color. Sherwin-Williams calls it "Java", I think I call it "oxide brown"!

Still waiting on the new idler. Sniff.

Sorry, the deck cover is a bit overexposed. Notice the tape sensor lamp now works! The plastic reel is there for show, and also because it had to be somewhere and that was better than on the floor... at least until I replace the idler and start pulling tape again.

The C37 pictures have inspired me to try winding without the flanges on the takeup hub, at least once I'm sure the transport is working exactly as it should. I guess you could call that a precision hub?

Cheers,

Otto

 

[ethyrvalve]

Wow Otto, that's truly a thing of beauty!
Why the 'bias' and 'erase' settings on the meter select? Do you set the erase bias and record bias separately?

 

[ofajen]

Wow Otto, that's truly a thing of beauty!
Why the 'bias' and 'erase' settings on the meter select? Do you set the erase bias and record bias separately?

Not normally. It's just a handy way to check to see what those test points are reading at. Each one has its own monitor calibration trim pot, so you can set it to 0 VU when things are right and then you can check back at some later time and see if it's pretty much still on target. Not something you need to use a lot.

Sadly, the pictures really don't do it justice. It turned out pretty nice now that the console is painted. I'm eager to get the new idler and fire it back up for what will hopefully be an easier electronic alignment process.

The M-23s are still perfectly good small format machines (1/4" or 1/2" tape). A 1" 8 track would be a little much: 300 pounds and very tall (four channels below and four above). They are a little clunky, in that they have the separate electronics for each channel, so they aren't so convenient for being multi-tracks, but for 1, 2 or 4 tracks they are fine. They can generally manage to do just fine with any tape, regardless of thickness and can operate up to +9 without too much electronic distortion.

At some point, I'm going to spend some money to bring Mitch's M-23 over here. He doesn't seem to fancy trying to rehabilitate it any longer, but if it's doable, I probably will. If someone could make me a reasonable deal on some 1/2" heads, I'd love to fix that machine up as a 4-track. I seem to recall JRF thought he could scrape up something reasonable for around $600 for the heads and two more channels of electronics.

Cheers,

Otto