Motorola ST-82A stereo AM-FM record player

[electra225]

Yeah, I know, this is the other "M".

I got this little stereo in a parts car I bought. I bought a '73 big Buick wagon for the engine and transmission to use in a GS tribute car. The back of this wagon was LOADED with "stuff". There was a part sheet of paneling there. Under that paneling was this stereo. I dug it out, plugged it in and it worked, only on one channel. One of the output tubes was dead, a 50HN5. This stereo is circa 1965 with codes of the 46th week and the 48th week of 1964. I also had the console version with the same chassis as this one. It has an eight tube hybrid hot chassis. I have the owner's manual, along with the various hang tags and turntable cover for it. This thing has traditionally been a good performer, although I haven't used it in a few years. IT has a VM 1200 series changer with what I believe is a Tetrad ceramic cartridge. Single-ended 50HN5 audio, rated at five watts. It currently has an extremely dirty and intermittent function switch and the pilot light is kaput. I believe it to be a neon bulb of some kind. This thing needs a good tune-up and cleaning. Probably the changer should be serviced, as well. I have a new needle for it around here somewhere......

[hermitcrab]

Wow! what a cool thing to find in the back of a parts car...I would have been giddy upon finding this ... Great score !

[electra225]

A friend gave me the console version. IT had ten inch speakers, in place of the six inchers in this thing. It was a very mediocre performer. IT sounded like what it was, a cheap console stereo. I don't believe this chassis was one of Motorola's better efforts. This particular one is a good performer. Not a lot of bass, but what would you expect with six inch speakers?

[William]

From your description, the Buick find Motorola sounds about like my Motorola portable that I have always complained about the lack of bass. Mine is a SE 6BQ5 five tube, big PT portable. It's well built and heavy but has 6" woofers with 4" tweeters in swing out speaker enclosures. It will blow you out of the room with volume, but there is zero thump to the bass.

Bill

[electra225]

This one is not blessed with volume that will knock your socks off, nor does it have massive bass. The funny thing about that rather pessimistic assessment is that it sounds quite pleasant in the final analysis. I've never done a thing to it other than replace one of the output tubes. The cord was dried out, so I swapped cords with the console before it went into the auction. The front end of the chassis is tube, the audio section is tube. The Multiplex circuit, ratio detector and the stereo light circuit are solid state. And the rectifier is solid state. This one may need a good recapping and a good control cleaning. The volume seems weaker than it should be. FM stereo operation is particularly good. The changer in this worked well last time I used it, but may need attention now.

[electra225]

I have been listening to Western Red this morning on the little Motorola stereo. I was fiddling around with wiring and got the pilot light to work. I have no idea what I did. Must be a bad connection someplace, on the "list" of things to do. The drive tire is getting pretty slick, too. For the first two or three times I started the changer, it took a minute to get up to speed. Then it wanted to stall when the changer cycled. So that is also on the list. Dirty controls seem to be the biggest difficulty with this stereo. An alignment might not hurt, either. The FM dial is dead under 100 mhz, with the exception of 93.9, where the local high-power FM station resides. It comes in faintly and garbled. I'll investigate the antenna, but I'm guessing that's not its only problem. AM seems especially "hot" for this type of instrument. Its loop antenna is somewhat directional. I was going to fix this up and try to sell it, but now I may keep it.

[William]

Remember my post about the 3 channel Motorola big table radio? I had what I thought was a dead stereo indicator lamp, it was neon. With the chassis outside the cabinet the light would not work. I tested everything I could think of and even tried a new bulb just because. Nothing worked, so I gave up and put it back into the cabinet. Once it was all back together, I fired it up and low and behold the stereo indicator lamp worked and has worked ever since. I have no idea why putting it back in the cabinet made it work, but I'm happy it did and now I'm enjoying my 3 channel Motorola table radio.

Bill

[electra225]

This one also has a lazy stereo indicator light. Maybe this is a Motorola malady?

[electra225]

I have decided to take this thing apart and go thru it. It has a lot of little things that need attention. The good side is that the cabinet is all hardwood, no particle board at all. I wasn't expecting that. I am in the process of removing the speakers so I can dig the dust out of them. I took lots of pictures so I can put it back like I found it, and will share those. I have everything out of the cabinet except the speakers.

[Hi-Fi-Mogul]

Greg,
Look forward to the spif-up of the little Moto.

That's nice that it is real wood.

[William]

Me too, on the progress and photos.

Bill

[Motorola minion]

Its true some Motorola stuff reminds me of GE, built to a price point. The styling is attractive enough.

The parts both manufacturer's used were better than average, thus these survived.

[electra225]

This little stereo appears to be well-built, I was surprised. It has a metal chassis with PCB inserts. The output transformers are fairly small, but what more do you need to work with 6" speakers? I was a bit surprised that there are no crossover networks on the speakers. The treble is plenty bright, so maybe they figured they could save a couple of pennies there. The console I had with the same chassis had a nice cabinet, but pretty wimpy performance. This smaller cabinet model actually sounds better than the console did. This thing must represent one of the last years Motorola built electonics with tubes. You'd know more about that than I do, Dave. What was the last year for tubes in Motorola stereos?

[William]

Greg, your Motorola reminds me of the GE I fixed for the people that own the antique store. It too was all wood and had swing out speakers. It was kind of the deluxe Swingline model. It could sit on a table or hang on the wall. It looked like this:

https://www.ebay.com/itm/164435049368

Bill

[electra225]

They are very similar, Bill. This one has fixed speakers, and a hybrid chassis, but those are about the only differences. The big plus on this one is the VM changer.

[electra225]

I have some pics here I'll share. This thing is almost as bad getting the chassis out as the Stereo Theater was. Wires are neatly arranged and routed, but are always under something else. I left the FM antenna alone, since it was stapled to the cabinet. Lots of one-handed reaching thru stuff to bring out the wiring.

[electra225]

I finally got the chassis out. I decided to clean up the speaker enclosures and the speakers a bit. I removed the speakers, vacuumed the cones of dust, then, using a detail brush and the shop vac, I removed as much of the dirt and dust as I could. Then I spritzed a small amout of Glance on a rag and removed the rest of the dirt in the cabinet. I followed this will a good dousing with lemon oil. I put a dab of Simichrome on a rag and got most of the gunge off the speaker baskets. The inside of this cabinet is very similar to that of a Magnavox Imperial or Concert Grand. All hardwood, no mystery wood.

There isn't much on the underside of the chassis. There is one 100uf @ 25 volt electrolytic there. The rest is ceramic disc and couplets. There is another cap like under the chassis on top of the chassis, you can see in the pics. The filter caps check fine, so they stay.

[electra225]

I haven't pulled any tubes with the exception of the audio tubes. The 12AX7 is branded "Telectro", made in Japan with what appears to be the Hitachi logo on it. The 50HN5 output tubes are more of a mystery. They are both branded Amperex. I don't remember putting Amperex tubes in this stereo. I remember changing one of the output tubes, but not both. The 12AX7 is in a pocket ahead of the cage around the output tubes and is nigh impossible to access with the chassis in the cabinet, at least for my old, fumbly fingers. Obviously, it is not original. I am suspicious of the condition of the 17C9 FM oscillator tube. I'll clean and test them all and check codes and that. I need to get a drawing for this chassis. I'm guessing it has two heater strings. A good AM alignment wouldn't hurt it, either. This thing has the healthiest-looking loopstick I think I've ever seen. IT is ALWAYS in the way when working on the chassis. I'll be lucky if the wiring survives my tinkering.......

[electra225]

I ran around doing errands all day today, but got a few minutes with this chassis. I found a schematic in the owner's manual. No parts list or alignment instructions, so I still need to find a Sams for this chassis. Model number HS-1323-D. There is a symbol stamped in black ink under the model number for the chassis "11-Motorola "M" symbol-64". I am assuming this to be the manufacturing date code, 11th month of 64. I don't know that's right, but it makes sense. I pulled the tubes and tested them. All checked good. I still may dig out a 17C9 and sub it for grins. The 17C9 is a Japanese-made Motorola branded, the 12BA6 is Motorola branded with an RCA code, the 12BE6 is a Sylvania, both 12AU6's are Motorola-branded, Japanese sourced. The speakers are coded 719, Carbonneau Industries. One of the 100Uf caps I found is the cathode bypass cap, the other one's purpose is still unknown. I need to study the drawing some more. I'm going to check resistors and generally give it a good going over. It has eight tubes, eight diodes, plus the rectifier, and three transistors. There is an 8uf at 25 volt cap in the MPX circuit I probably should replace. There are a couple wires, one blue, one green going to both output tubes that look like parts of them has been hot. Tube heat, maybe? It is in a very tight area.

[Motorola minion]

The last of big Motorola consoles with tubes AFIK was 1965 models, like your little one. It may have been a wall-mounted novelty model sold in the same catalog as the first all-SS higher-priced consoles. The 17C9 and tuner look RCA, the LAST good FM tube, shield between sections, connected to the 10th pin being in the center. I guess Motorola quit using the cast aluminum German-made ones using 12DT8 and before that, 6BQ7A, etc.

It seems as though they were multi-sourcing tubes for new radios in 60s, becoming less in demand as transistors replaced them in radios by 1965-66, way before all-SS TV in the early 70s.

The knobs and control design look like my SKR151, dated 10M63.
My '63 Motorola AM table radio has multi-sourced tubes all branded Motorola. All the ones in my '63 SK112, dated 8M62, seem to be Tung Sol.
The days of the "three pointed crown" and M in oval symbol, were indeed the last tube days