Motorola 77XM AM/FM Radio found today

[dieseljeep]

Originally Posted by Captainclock

Interesting, I hope this isn't going to need a lot of realignment because I really don't know a whole lot of realignment stuff except for just what I can do by ear, I have an oscilloscope which could be used for that but I don't have a frequency generator (I had seen one once at one of the local flea markets for $20 but I didn't have the money on me at the time and when I did have the money later on I went back to go get it and it was already sold!) Anyways What is Fremodyne? And why would they use the old FM (42-50 Mhz) as the basis for this radio which uses the modern FM band? Also the FM Tuner mechanism is really interesting on this radio it uses a "piston" like mechanism that's controlled by a small gear that's mounted on the AM tuning capacitor for tuning the FM...

The set uses the slug-type tuning principle. They were a bit more stable than the regular tuning condenser. Many of those early FM sets could be aligned with an AM signal generator, by following the proceedure in the service notes. I wouldn't bother with FM alignment, as it wouldn't help that much.
The Fremodyne was a form of super-regenerative circuit, developed for inexpensive FM receivers. Heathkit, even made a kit form in the late 40's. It received FM stations, but it wasn't a true FM receiver. Fidelity wasn't that great, as it used some form of slope detection.

[Captainclock]

Originally Posted by dieseljeep

The set uses the slug-type tuning principle. They were a bit more stable than the regular tuning condenser. Many of those early FM sets could be aligned with an AM signal generator, by following the proceedure in the service notes. I wouldn't bother with FM alignment, as it wouldn't help that much.
The Fremodyne was a form of super-regenerative circuit, developed for inexpensive FM receivers. Heathkit, even made a kit form in the late 40's. It received FM stations, but it wasn't a true FM receiver. Fidelity wasn't that great, as it used some form of slope detection.

interesting, so the way this radio sits currently it may be fine without a realignment needed? Fascinating. Anyways I think I'll just replace the power cord and the capacitors and go from there. I noticed that the orginal bulb for lighting the dial was a colored C7 style Christmas light bulb that was yellow in color but most of the paint flaked off over the years. I was thinking of experimenting with different color bulbs in this radio like with red, or blue or even green to see what kinds of different effects I can get from the radio dial. What do you think? It would be kind of like how some people put different color bulbs into old stereo receivers to make the ordinarily white glow tuner into a more interesting blue or green glow dial.

[dieseljeep]

Originally Posted by Captainclock

interesting, so the way this radio sits currently it may be fine without a realignment needed? Fascinating. Anyways I think I'll just replace the power cord and the capacitors and go from there. I noticed that the orginal bulb for lighting the dial was a colored C7 style Christmas light bulb that was yellow in color but most of the paint flaked off over the years. I was thinking of experimenting with different color bulbs in this radio like with red, or blue or even green to see what kinds of different effects I can get from the radio dial. What do you think? It would be kind of like how some people put different color bulbs into old stereo receivers to make the ordinarily white glow tuner into a more interesting blue or green glow dial.

The original lamp was probably white or clear.

[Captainclock]

Originally Posted by dieseljeep

The original lamp was probably white or clear.

I'm not hearing any objections so I guess I will then try out some different colored bulbs then.

[old_coot88]

The candelabra-based 'Xmas tree' bulbs commonly used in 'nite light' applications are very short lived, unlike the originals. Even with a diode in series to run them at half power they burn out quickly.

[Captainclock]

Originally Posted by old_coot88

The candelabra-based 'Xmas tree' bulbs commonly used in 'nite light' applications are very short lived, unlike the originals. Even with a diode in series to run them at half power they burn out quickly.

SO basically any of the modern "nightlight" bulbs which is what this uses (except that the original was a 10 Watt bulb according to the Rider's service Information which they don't make 10 watt nightlight style bulbs anymore and the next closest would be either a 4 or 7 watt bulb.) what I would and could do is try and find a box of NOS C7 Christmas light bulbs (which they do show up quite often at the antique malls near me, especially around Christmas time) because it seems that's what you're saying by saying that the older ones lasted longer than the modern ones do.

[old_coot88]

In my experience, the 4 and 7 watters made in the last 30 years or so are very short lived.

The original 10 watters used in the 'Exit' signs in my building, installed in the 1960s, lasted a good 20 years before they started burning out. The only replacements available were the 4 and 7 watters, which required constant replacement until I finally got rid of them recently and put in LED retrofits.

And BTW, before somebody hollers, I did not run the 'Exit' signs at half power. I ran a single bulb with a diode to test how long it would last, and it burned out almost as fast as without a diode.

[dieseljeep]

Originally Posted by old_coot88

In my experience, the 4 and 7 watters made in the last 30 years or so are very short lived.

The original 10 watters used in the 'Exit' signs in my building, installed in the 1960s, lasted a good 20 years before they started burning out. The only replacements available were the 4 and 7 watters, which required constant replacement until I finally got rid of them recently and put in LED retrofits.

And BTW, before somebody hollers, I did not run the 'Exit' signs at half power. I ran a single bulb with a diode to test how long it would last, and it burned out almost as fast as without a diode.

My job, as an electrician on second shift was to do exit lite maintenance. Lamp life was highly dependant on how well the filament was supported, which is true with just about any incandescent lamp. They used to buy 130 volt lamps. Some signs used low wattage fluorescent lamps.
At the end, we installed LED signs with ni-cad battery backup. That's the kind, I have in my two buildings.

[jr_tech]

I Use these LED bulbs on my vintage night-lights and radios that require a line volrage bulb. They work fine for me and run very cool (only .36 watts!).

http://www.amazon.com/G7-Power-Beatt...ight+led+bulbs

not affiliated,
jr

[bandersen]

Originally Posted by Captainclock

...There was someone else that had this same exact radio on here that they overhauled and I was wondering if whoever that was might be able to chime in and give me some tips....

Nice find You might be thinking of me. Mine was partial recapped and partially working when I received it. I haven't had a chance to finish restoring it yet.

http://www.videokarma.org/showthread.php?t=260088

[Captainclock]

Originally Posted by bandersen

Nice find You might be thinking of me. Mine was partial recapped and partially working when I received it. I haven't had a chance to finish restoring it yet.

http://www.videokarma.org/showthread.php?t=260088

OK, I thought someone on here had one as well but wasn't sure who which is why I asked. Anyways how was the cord repaired on yours or does yours still have its original cord still intact?

[Captainclock]

Originally Posted by jr_tech

I Use these LED bulbs on my vintage night-lights and radios that require a line volrage bulb. They work fine for me and run very cool (only .36 watts!).

http://www.amazon.com/G7-Power-Beatt...ight+led+bulbs

not affiliated,
jr

I might give that bulb a shot once I get the radio up and running.

[wa2ise]

Originally Posted by jr_tech

schematic on page 1 & 2

https://www.tubesandmore.com/schematics/motorola/hs-102

hs-102 is the chassis number for the 77xm.

First time I've seen a radio make use of the AM pentagrid converter 12BE6 tube as an FM IF stage. I figured that that would be possible, and sensible, to put that tube to work when the radio is in FM mode. Don't know why this wasn't done more often. You'd need a switch contact that disables the AM local oscillator. Just short the cathode portion of the osc coil.

[bandersen]

Originally Posted by Captainclock

OK, I thought someone on here had one as well but wasn't sure who which is why I asked. Anyways how was the cord repaired on yours or does yours still have its original cord still intact?

Luckily, it still has the original. The third wire ends just short of the plug. I'd use a modern three wire electrical cord with a two prong plug. Use the third "ground" wire for the antenna.

[Captainclock]

Originally Posted by bandersen

Luckily, it still has the original. The third wire ends just short of the plug. I'd use a modern three wire electrical cord with a two prong plug. Use the third "ground" wire for the antenna.

OK Thanks. That's what I was thinking of doing myself but I thought I would get a second opinion from someone on here first. I'll probably take a trip to the hardware store this afternoon and see if I can find the kind of cord I need.