Prewar Radios with "TV Sound" on the SW band

[Steve McVoy]

A recent thread at rec.antiques.radio+phono:
http://groups.google.com/group/rec.a...a7aa08a09859bd

uncovered that some radios made in 1940 had the notation "TV Sound" on the tuning dial on the shortwave band at just above 8 mHz. Philco made a "television converter" in 1940 which broadcast the audio IF (8.25 mHz) to a nearby radio receiver, thus eliminating the need for an audio detector, amplifier, and output tube:

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

The notations have been discovered on Sears/Silvertone models 6436 and 6490. Probably 1940 model Philco radios have similar notations.

If you have a radio with TV Sound on the SW band, please post it here. I'd like to see how many manufacturers did this.

[polaraman]

My 1939 RCA T63 says "designed for television attachment." I do not see Tv sound on the SW scale. What is AM'T'R?

I can also add that our current military 2 way communication radios can pick up TV audio. Comes in handy while in the field and the World Series is going on.


polaraman

[ChrisW6ATV]

Originally Posted by polaraman

What is AM'T'R?

polaraman

Probably refers to Amateur ("ham") Radio. The frequency bands would be perhaps 1.8-2, 3.5-4, 7-7.3, 14-14.35 and 28-30 MHz depending on the coverage of your shortwave receiver.

[Adam]

The SW dial on this Philco radio only goes up to 3.3MHz, but there's a sticker on the back that says " BUILT TO RECEIVE TELEVISION SOUND - The Wireless Way - when used with Philco Television Picture Receiver, without Wires, Plug in, or Connections of any kind "

[Jukin Jay]

From this thread it seems as if there were three separate schemes. The RCA radio had an RCA plug (so named...) for a wired audio connection. These also worked with their cute 45-RPM record changers.

It sounds as if the Philco was intended to be used with Philco TVs that probably were intended to include a low-power transmitter in or near the broadcast band.

The 8.5 MHz sound IF pickup sounds implausible. Even in the early TV days the sound was FM, and the AM/SW radios were AM. Also the TV IF strip would need to be very well shielded to avoid oscillation if it was intended to radiate far enough to be heard on a nearby radio.

I think that the claim of "Ready for TV" on radios of that vintage was more marketing than technology. Television was in its infancy, an expensive novelty. Manufacturers could sell more radios if the consumer had a notion that a "simple adapter" soon to be available would allow them to get video on their brand new radio.

On the other hand I think I read here of a limited number of very early televisions produced without an audio output stage or speaker. These were indeed intended for use with the amplifier and speaker of a companion radio. The RCA scheme makes the most sense to me, much like the "AUX" jacks on 1970s stereo receivers are happy with CD players and IPods that didn't exist at the time the receivers were produced.

Did Philco ever manufacture a TV set sans audio stage that coupled to their radio "The Wireless Way"?

[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

[Steve McVoy]

Thanks, Darryl, for correcting my information on the RCA set.

[Steve McVoy]

I've posted a page with more information on TV sound, along with a technical manual for the RCA RR-366.

http://www.earlytelevision.org/wireless_tv_sound.html

http://www.earlytelevision.org/rca_rr366_manual.html

[similost]

Here's a page from the manual that came with my 1940 (built in 39) Zenith console.

While it's not "wireless" nor meant to recieve on SW, they must have seen TV sound needing to be output to something to be heard would be my guess...


anyway, here's the manual page. It's an 8s563

[wa2ise]

TV sound was orginally to be AM. But just after WW2 the FCC decided to bump up the scan rate from 441i to 525i, and make the sound FM. Which annoyed David Sarnoff of RCA no end, as that would require RCA to pay licensing to Armstrong, the guy who invented/developed FM. But the FCC was correct in mandating FM sound for TV, AM would have sounded like crap, with much interference from the video sidebands of the TV signal.

[Steve McVoy]

FM allowed intercarrier sound, which would have been impossible with AM. AM would have sounded fine as long as separate IF sections were used.