Classic Hifi Care

I have a Motorola ST-82 "portable" stereo and its stereo indicator light works much like you have described. There is a 17C9 ten contact, nine pin tube in the front end of the tuner. When I replaced that tube, not only does the FM band work better, but it seems to have made that indicator light work MORE like it should. I have read other owners of Motorola equipment who have expressed frustration with getting the indicator light to work more like they believe it should. Maybe it's the nature of the beast?

I wonder if the stereo light dysfunction may be related to RF interference from all of our modern stuff, which did not exist in the 1960's, especially if it's functionality is affected by changes/improvements in the FM front end as Electra225 mentioned. Just the WIFI floating around in my house might be sufficient to scramble the radio RF design parameters.

One thing I just found out: my Bluetooth arrangement definitely causes some noise/distortion in a stereo FM station (but has no apparent effect on the stereo light). The built-in FM antenna is just a single wire that runs around the back inside of the cabinet, right next to my Bluetooth adapter! I'm going to experiment with placement of the Bluetooth box, and maybe also rig up a simple dipole for the back of the cabinet. If it continues to be a problem, no big deal I guess, since FM will rarely be used.

I think I'm finished with this guy for now! I deoxed the inline 3-pin connector for the stereo indicator lamp, because it seemed to be an issue--I think I forgot to clean that one before. So, the light comes on all the time, pretty much, even off-station. But, the stereo separation was virtually zero. The uploaded doc that I mentioned above has a helpful description of the way the MPX works, and alignment procedures. So, I connected a DVM to the test point, and peaked the coil and transformer as instructed, I got about 33 VDC, give or take. But to max out the stereo separation, there is a more complex procedure described which would mean I would have to open up the MPX again. Instead, I just listened for stereo separation on a strong station (putting my head centered at the back of the console), and tweaked L3 to where it seemed max, that setting was off the peak voltage, ended up around 28V or so. Not a perfect procedure, but separation is much better than it was before, and it meets my needs! Those inductors are labeled differently on other schematics that I have, but the basic functionality is the same.

When I attached the dipole for the FM antenna and disconnected the long wire that originally served as the OEM antenna, the interference from the Bluetooth adapter went away. I'm guessing that's because the antenna system is now balanced--before, the OEM wire just attached to one side of the 300 ohm antenna input which must have made it more susceptible to interference.

https://photos.app.goo.gl/wWBDFVNypWmLgYkt9

Hopefully this link will work OK, since it is a link to my personal Google storage. Playing on the changer is the Cincinnati Pops Big Band Orchestra "In the Mood", switching to Tape input is Jerry Lee Lewis "You Win Again" (his recordings have his voice way too loud!). I also show a 4-input switcher I attached to the back. I decided to bring the tape input connection out the back to allow me to hook in other audio sources besides Bluetooth (which is #1 on the switch). The lid is still a little warped, gotta keep working on that!

The FM stereo light continues to give me problems, it is now not working at all, even thought it was OK when I buttoned up a week ago! I now suspect that it may have to do with the IF alignment of the tuner--I've read that early stereo tuners had to be redesigned to make sure the 38Khz pilot would get through on its way to the MPX, so alignment is probably critical. I'm not inclined to tackle that right now!

As I mentioned in the Changers section, I finally replaced the motor mounts after hearing the motor noise when I made an earlier video. The phone's mic is omnidirectional, so it picks up all the reflected room acoustics, but that really emphasized the motor noise, and makes the console sound somewhat "boomy". This video is made with the new mounts.

I have suspected alignment and antenna efficiency as being a part of the stereo light issue, but, like you, I hesitate to mess with that. I figure a wonky stereo light is just part of its personality......

Do you hear stereo with the light out? That would tell whether the problem is switching or just illuminating the lamp. I have a little inexpensive GE receiver next to this computer driving a couple small Polk speakers. The light came on but I was not sure until I heard something way off on the right....

Chris Campbell

It looks good and even though I am listening to it on crappy computer speakers it sounds pretty good too. I still say all Motorola FM stereo lights work weird. Good job, what's your next project.

Bill

Unfortunately, Chris, when the stereo light is off, it's mono, there is no stereo separation, so it's not so simple

In the background, I've been working on cleaning up my old AR XA turntable and adding a preamp to it, plus getting my Sony TC-377 tape deck running again. But I plan to get back to work on my 1948 Olympic soon, spruce it up and try to sell it. I'm thinking about adding a Bluetooth adapter to it also, even though it's mono, maybe make it replace the AM position on the selector switch. We shall see......

That Olympic doesn't have a phono input? If it does, then it's likely for a crystal cartridge, a high-output device with a relatively low-gain input. Put the Bluetooth there, and save the AM option! One of my guilty pleasures is tuning in WSM from Nashville on a Saturday night, live from the Grand Ole Opry, just as many famous musicians, black and white, did as kids. Like Ray Charles.... It helped our regional and ethnic music genres interact and influence each other. There's something magic about that little signal coming through the air from about 700 miles away, for me, bringing music with it.

Many of those folks were listening on "farm radios," either 6V vibrator-supplied radios with windmill generators, or ones with B+ and A batteries.

Chris Campbell

Chris, which one of your radios consistently pulls that station in and what number on the dial?

Thanks,
Bill

WSM is at 650 AM. 50,000 watt, clear channel station.

Thanks, Greg.

Bill

My oldest working radio, a two-tube 1924 Crosley received WSM on a long wire antenna! I usually listen on my GE P-780, a mid-50s classic portable. It sits inside the big loop antenna, although it receives pretty well without it. It was designed for good reception and good sound, as portables go. The restored GE E-86 sounds even better. I'll hook it to the long wire, although noise from the neighbor's outdoor LED lights sometimes makes a mess.

WSM sits there at 650 kHz all on its own. It has been broadcasting the Opry since 1925, which makes the Crosley an appropriate receiving device.

Chris Campbell

Thanks, Chris. A two tube radio blows my mind and it can pull in a station that far away. Amazing!

Bill

It uses regeneration, basically feeding the RF signal back again for more amplification . It's very similar in that regard to my Knight-Kit Space-Spanner, a regen. device with 2 audio/RF tubes plus a rectifier, since it's AC powered. The Crosley was designed for A & B batteries. I have an ARBE power supply.

Chris Campbell

I typed a response to this topic, then I realized we were really taking our liberties with topic integrity. Sorry for stomping on your topic.....

Back on topic,
The crystal phono input does indeed work with the Bluetooth adapter, but I would have to add a switch to allow selecting either phono or Bluetooth. I doesn't work to have them both connected in parallel.

Also, my target market for this unit will not be interested in AM, especially not AM DX-ing! And, this unit does not have a decent built-in AM antenna, just a wire loop stapled to the back of the cabinet, not a nice high-gain, rotatable loop as shown in the Sam's data!

If I make this mod, I will arrange the new Bluetooth input wiring with RCA plugs so AM can be reconnected if desired. Since it's a 78-only changer, I will be a tough sell anyway, but I don't want to have to replace the changer.

stbasil wrote: ↑Sat Feb 15, 2025 3:20 pm Back on topic,
The crystal phono input does indeed work with the Bluetooth adapter, but I would have to add a switch to allow selecting either phono or Bluetooth. I doesn't work to have them both connected in parallel.

Also, my target market for this unit will not be interested in AM, especially not AM DX-ing! And, this unit does not have a decent built-in AM antenna, just a wire loop stapled to the back of the cabinet, not a nice high-gain, rotatable loop as shown in the Sam's data!

If I make this mod, I will arrange the new Bluetooth input wiring with RCA plugs so AM can be reconnected if desired. Since it's a 78-only changer, I will be a tough sell anyway, but I don't want to have to replace the changer.

I'm confused. Which player are you discussing here ?
It obviously isn't the SK111W topic, correct ?

Sorry for the confusion, the question was asked, before the off -topic discussion, what my next project is, and I was referring to my 1948 Olympic.
So, no, my SK111 is a keeper!

That Olympic is nice! I think I'd be prone to putting a stereo changer in it. I've tried Bluetooth, and I can see why people like it. But for me, someone who uses a cellphone for an appliance, not a lifestyle, it is more trouble than it's worth. If I put Bluetooth on my old stereo, what do I do with the hundreds of records I have?