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City: Sandwick, BC, CA
Hi All;
I just picked up an oddball AC/DC set via craigslist called a Medco which was apperently made by a company called Telephonic but I can find no reference in the Rider manuals to either name. It has six loctal tubes types , 35Y4, 35A5, 14B6, 14A7 (12B7), 14Q7, and another 14A7 (12B7), my guess is that it was made between 1946 and 49. I can't find a model number or any markings on the cabinet or the chassis but it has a solid wood cabinet (no veneer), a square airplane dial, two knobs, and is broadcast band only. I found a photo of a similar set online called a model 1635 but I have no way of knowing if it's the same model.
Regards
Arran
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City: Montreal, Qc
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Arran Wrote:........ a Medco which was apperently made by a company called Telephonic.....
The only Medco's I could find were made by Telesonic, and the only schematic reference I could find was for Sams #20-22 for model 1635. Unfortunately I haven't collected any Sams so I can't be of help making a copy.
John KK4ZLF
Lexington, KY
"illegitimis non carborundum"
Posts: 4,612
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Eliot Ness Wrote:Arran Wrote:........ a Medco which was apperently made by a company called Telephonic.....
The only Medco's I could find were made by Telesonic, and the only schematic reference I could find was for Sams #20-22 for model 1635. Unfortunately I haven't collected any Sams so I can't be of help making a copy.
Yes that's right, Telesonic, I must have been think of another set that I have called a "Symphonic", made by another short lived radio manufacturer. In any event someone on the other forum lined me up with a Sams Photofact schematic so I have proceeded with the restoration work.
I was a good thing that I stopped when I did and waited until I had the service data in hand, someone has really messed with this radio and it isn't exactly like your typical AA5 or 6 in the power supply circuitry. While I was going over the set last night I was finding so many errors that I ended up stripping half the set down to the bare sockets, the front end wasn't bad but the power supply and the audio circuits were a disaster consisting of random parts salvaged out of someone's junk drawer. What I think happened is that someone tried to repair the set and then made a half hearted attempt to convert it over to a floating chassis design by isolating the B- line from the chassis.
They only did it about half way and the power line was already partly isolated from the chassis in that there is a series of resistors between the power line and the chassis. The first filter cap has a floating ground, then a pair of 50 ohm resistors between the negative of the first filter cap and the second filter cap, the negative end of the second filter cap is connected to the chassis. Connected to the junction between the two 50 ohm resistors is one end of a 2 meg ohm resistor to supply bias elsewhere in the set. It's rather weird to see a bias network like this in an AC/DC set, it more the type of thing that you would see in an AC radio from the 1930s. Whoever was in there last completely ignored this setup and connected the negative ends of both filter caps directly to one side of the power line, and add other things like adding a cathode resistor to the power output tube where there wasn't any. I don't know if this set ever played properly if at all with what they did so I am going to put it back to the way the factory made then maybe figure out how I can isolate the B- after I get it going, if it's worth the effort.
Regards
Arran
