Motorola ST-82A stereo AM-FM record player

[Hi-Fi-Mogul]

Greg,
I found the Sams's 790-6, which appears to be
your schematic.

Interestingly, the photo of the cabinet on the Sams
is of a console.
Reading the speaker parts list, I noticed your
ST-82 model number there.

Post here when you PM me with an email, and I'll send you the file.

[electra225]

PM sent, Mr. Mogul and thanks!

Thanks for the information, Dave. With a code of 11th month of 1964, this may be one of the last tube stereos Motorola built? Cool....

[electra225]

Mr. Mogul was kind enough to send the Sams for the little Motorola stereo. I need to order parts, I see. Thanks, Mr. Mogul for your kindness!

[electra225]

I finished the electronics this afternoon. I changed the elusive C3, which is a 50uf @10 volts electrolytic in the Multiplex circuit. I changed the cathode bypass cap and an 8uf@ 25 volt electrolytic in the Multiplex circuit. I have the chassis back in the cabinet and am in the process of cleaning the wiring and putting it all back. Motorola runs their wiring very neatly, certainly compared to Magnavox. I removed the base for the changer and cleaned it all well. Next up, after finishing the wiring, is the changer.

[electra225]

Well, at least I THOUGHT I was done.....

I turned this little stereo on to listen to Western Red this afternoon. On AM radio. It played about 15 minutes, then the volume faded to nothing. FM was fine. Remember, I had no FM on the lower end of the band when I took it apart. AM was working almost fine. I can explain the "almost". When the radio faded, I unplugged it. As I pulled the plug, the volume shot up, then died when the tube filaments went cold. I plugged it back in and the AM radio worked. It played about another 15 minutes, then faded again. FM was still okay. The AM converter tube was a Sylvania 12BE6. I tested it, but on converter tubes, as they can be a finicky lot, that is not always an accurate test. I pulled the converter tube and inserted a tube I keep for test. The radio played for three hours with nary a hitch. I tossed the original 12BE6. I hope this fixes it. I'll let it cool really well, then try again. Stand by......

[Hi-Fi-Mogul]

Boy, haven't we all been there with "I thought it was done ", ha ha !

I hope the tube was the only glitch there Greg.

[electra225]

I have developed the habit of "storing" the cabinet back of an instrument I recently "fixed" behind the instrument, unattached, for about six months. I hate wearing out the holes for the back screws simply because I can't fix it right......

Yeah, I get kicked by that mule several times a year......

I'm glad to know I'm not the ONLY one......Thanks, Mr. Mogul......

The changer is next. I'm almost done. I have pictures. Stand by.......

Oh, and another thing, I forgot. The balance control on my old standby, ultra-dependable 1ST616 has decided to act up. I reckon it must be dirty. One channel went totally dead until I tinkered a bit. I'll have to pull the tuner to clean the balance control...

[William]

I usually do the same thing, Greg, I leave the back off just in case. Of course, with the Imperial you can't do that because of the dumb way Magnavox did their speaker connections. Also, the balance control on my Symphony appears to be dirty as well. For some reason, all of a sudden, one channel is weaker than the other and when I try to adjust the balance control it won't find center. I guess we are in the same boat at the same time.

Bill

[electra225]

Your Imperial should work with the back off, with the speaker wires disconnected. The wires on the back are for external speakers. The main console speakers are wired through the Molex connector.

[William]

You would think so, but for some reason mine does not work that way.

Bill

[electra225]

I have some pictures of the changer. VM model 1267.

Motorola uses an Alliance motor. The GE's I have use a GI motor on their VM changers. Moto must has spec'd a better motor?

This is allegedly a Tetrac cartridge. Perhaps some of the cartridge gurus on here could straighten my thinking on this.

I found the box with the new needle. In that box, was a set of new motor mounts, so that worked out nicely. This is a really clean changer, I believe with low hours. The motor bearings were still nice and shiny. I gave it a good cleaning and lube, put it back together. The drive tire was still pliable, so I gave it a good cleaning and a light sanding.

[electra225]

The only device that holds the platter on is a white o-ring?

The platter mat has a button in it almost on the edge. What is the purpose of the button?

[Hi-Fi-Mogul]

The only device that holds the platter on is a white o-ring?
The platter mat has a button in it almost on the edge. What is the purpose of the button?

Greg,
1. Yes that is a Tetrad cartridge, a special narrow
design for that particular Moto tonearm.
I've seen that tonearm in a few Moto consoles of same era.

If the cart ever fails, Gary at the V of Music has a way to
install another Tetrad. The original Tetrad is
no longer obtainable.

2. Yes, the hard rubber O-ring is the platter retainer.
I had the same reaction when I first learned that.

3. The platter button is the for 7 inch record size sensor.

[electra225]

Thanks, Mr. Mogul. I wondered if the button had something to do with the size of record. And I'm glad to know the cartridge is a Tetrad. I had guessed that it was "unobtanium" just by its design. I don't know what the tone arm weight is, but it is pretty light. I'm guessing maybe lighter than the EV 26 tracks in a Collaro changer? The platter mat is fairly plain, devoid of any bright trim. I'm wondering if one of the "prettier" more trimmed mats Gary has would work on my changer? I'm guessing that if I get one for about any VM changer it should work?

[Hi-Fi-Mogul]

The platter mat is fairly plain, devoid of any bright trim. I'm wondering if one of the "prettier" more trimmed mats Gary has would work on my changer? I'm guessing that if I get one for about any VM changer it should work?

Greg,
Gary has a section just for you. Mats and mat trim pieces
to make it as cool as you wish.

https://thevoiceofmusic.com/catalog/vm_ ... s_more.asp

[electra225]

I looked on Gary's site. I wondered if almost any 11" mat with a button would work on this changer.

I will have to admit that I under-estimated this little stereo. Going thru it, changing capacitors, cleaning tube sockets, changing a tube or two, cleaning the controls and changing the needle really brought this thing to life. It is a worthy competitor to Magnavox. I have never been a Motorola fan, but I am now. I have been playing a Readers' Digest six-record compilation of Lawrence Welk material. "Made for Readers' Digest in Cyclonic Miracle Sound by Radio Corporation of America". Lawrence Welk on RCA, something not all that common. Judging by the material that is presented, I'd say this record was from the middle 1960's. Frank Scott is still with the band. Plus, this record is in hyper-stereo. There are a myriad of sounds on an LW record, perfect for wringing out a new stereo. The changer works perfectly. If I had a complaint, it would be that there seems to be a lot of changer rumble. Maybe that can be expected when running a two-pole motor. Not horribly objectionable, but it's there in the lead-in strip on records. One time, the needle dragged across a portion of the record when it changed discs, so maybe I need to make an adjustment of some kind. It only did it once. It shuts off after the last record. So, my changer tune-up is not perfect, but I didn't kill it, either, so that is progress for me. And, just for the record, it's not for sale anymore........

[Hi-Fi-Mogul]

Check that the tonearm wires have plenty of slack,
for the tonearm arc of travel.

At some point, it would be good to do a dis-assembly
and cleaning of the main parts of the cycle mech.

Small amounts of old dried grease can
create subtle or greater problems.

[electra225]

There is a little plastic bolt/screw under the tone arm that apparently adjusts how high the tone arm lifts. I gave it a quarter turn. It doesn't take much to make a lot of difference. It seems better the more records that get stacked on the spindle. I don't know how many the limit is, but I stacked six and didn't have any trouble. I have the service instructions for VM changers that I consulted to see what I needed to do. Taking the mechanism apart is out of my wheelhouse at this point. Maybe sometime down the road. I'm learning in baby steps how to work on changers. There was a time in the not-too-distant past I wouldn't have attempted even this much. I appreciate everybody giving me the benefit of their knowledge on changers.

I gave the mechanism a "shower with your socks on" kind of clean and re-lube.

BTW, I have a spare Admiral thingy that shows how the VM changer works. I found it under the Motorola one on this stereo. If anybody can use it, let me know.

[William]

Ok, what's an Admiral thingy?

Bill

[electra225]

Jeez, Bill, you are Mr. VM and don't know what an Admiral thingy is?

It is a paper they put on the platter as an advertisement gimmick when the device was still on the showroom floor. A demonstration piece if you will. The Admiral one I have is 11" in diameter. It is part of the documentation on a device that people like to collect and show with their instrument. I have Magnavox and Motorola, but don't really need the Admiral one. If anybody could use it, that would be great.

And, to answer Mr. Mogul better, I have a spare VM changer that I am planning to get a little deeper into. This instead of one in a device I am using.