Prewar Radios with "TV Sound" on the SW band

[Steve McVoy]

There were only two ways of using radios for TV audio that I'm aware of. First, and most common, RCA and GE bottom of the line 1939 and 1940 sets (TT-5 and HM-171) had an audio detector and a jack on the back to connect them to the TV inputs (RCA jacks) provided on a number of prewar radios.

The second was the one used by Philco in their 1940 7 inch TV set, which had a low power 8.25 mHz transmitter. TV until 1941 had AM sound, so a standard SW radio tuned to 8.25 mHz would receive the sound from the TV set. Silvertone had a mark at 8.25 mHz on their SW dials.

Here is the Philco TV set that used that appproach:

http://www.earlytelevision.org/philc...html#converter

I just learned that RCA produced a prototype 5 inch receiver, the RR-355, which used the 8.25 mHz approach. A few of these were made for the 1939 World's Fair, but none were ever sold to the public.

Silvertone, and probably other manufacturers, included a marking on the SW dial at 8.25 mHz for this system. This approach would not have worked very well, since any drift in the TV local oscillator would have moved the IF frequency, and therefore the SW radio would have to be retuned.

I know of no TV set that used a low power AM band transmitter for the sound.

[tubesrule]

The RCA set was the RR-366 prototype from 1937. It used an 8.75MHz IF that was broadcast to a nearby radio. There were only three of these sets made.

Attached is a page from the manual for the set.

Darryl