Motorola 77XM AM/FM Radio found today

[Captainclock]

Originally Posted by truetone36

That's not a 50's model, it's from 1948.

OK well I kind of figured that out after I posted this thread because I looked at the riders and even after seeing that the pilot lamp was a 110v night light bulb like my 1946 philco was I realized it was probably 1940s and not 1950s. I'm guessing that since this has Modern FM on it besides AM that must mean this was a higher end unit since most radios from 1948 were either AM only or AM and Shortwave only and no FM.Either way besides the cord being gone on it the unit is in fairly good shape yet surprisingly enough, and is complete.

[dieseljeep]

Originally Posted by Captainclock

OK well I kind of figured that out after I posted this thread because I looked at the riders and even after seeing that the pilot lamp was a 110v night light bulb like my 1946 philco was I realized it was probably 1940s and not 1950s. I'm guessing that since this has Modern FM on it besides AM that must mean this was a higher end unit since most radios from 1948 were either AM only or AM and Shortwave only and no FM.Either way besides the cord being gone on it the unit is in fairly good shape yet surprisingly enough, and is complete.

I looked up the schematic on N/A and was surprised to see it still used the 4.3 mhz IF frequency, like the pre-war FM sets used.
Those early FM sets weren't that good of a receiver, plus they drifted like mad.
Well, at least it isn't a Fremodyne!

[Captainclock]

Originally Posted by dieseljeep

I looked up the schematic on N/A and was surprised to see it still used the 4.3 mhz IF frequency, like the pre-war FM sets used.
Those early FM sets weren't that good of a receiver, plus they drifted like mad.
Well, at least it isn't a Fremodyne!

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...

[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.