[morzh]

Hey guys, A fellow-radio collector from a Russian forum contacted me asking if I could provide infoprmation about the highest possible frequency America radios used before the WWII (those made before the US entered the war I think would be correct interpretation as this was the event that put some radios on hold and then changed some technology once the war had ended).
Let's make it 1939-1942 divide between pre war and 1945 post war.

The exact question is: was there 30MHz or 50MHz band before the WWII?
And when exactly we started using those?

Even more exact: could pre-war radios gop into 50MHz in principle (was the technology available, like proper tubes and such), and where there 30MHz radios before the war?

I am not that good with hostory of the US tube radios, but I am sure many folks here are.

[Doug Houston]

High frequencies were known before WW II in several places. For home radios, FM broadcasting began in 1940, and used the frequencies from 42-50 Megacycles.

Then, television channels picked up after the FM band, and prewar channel 5 became postwar channel 4 (66-72 Magacycles). I'd need to look it up, but there six prewar channels, so the TV spectrum went a tad higher than the old channel 5.

Now, Hallicrafters made two models (actually the same set, cepackaged) the models S-27, and S-36. Both covered from 27 Megacycles to 155 Mc. Both sets had AM or FM reception.

Then, the Halli. S-37 picked up after the S-36, and went all the way to 216 Megacycles, which was the top of old TV channel 13 (210-216 Mc).

Tube technology was the key to high frequency performance. The first 7 pin miniature tubes were beginning to appear just prior to WW II for us, the tubes that made high frequency use possible were the "acorn" tubes: 954, 955, and 956. These were in the front ends of those Hallicrafters sets just mentioned.

The front end of the TV sets had to be content with a 1852 (6AC7) mixer,, and 6J5 Oscillator. They worked, to the surprise of many, even RCA, we can bet.

The new 7 pin jobs were: 9001, 9002, 9003. there was also a good little RF tube: 6AK5, before the war.

Loktal tubes, pioneered by Sylvania, proved to have superior performance to many (most) octal based tubes at high frequencies, because of their revolutionary new interior design. But RCA would never have been caught dead, using another company's tubes, so they never used Loktal based tubes.

[codefox1]

Hal GhZ easily done.

[TA Forbes]

The top band on a Philco 37-665 and 38-665 was 25 to 42 MHz.

The top band on the RCA 262/263 was 11 to 36 MHz.

[morzh]

Thanks guys, very informative and thorough.

[Radioroslyn]

Well Done Doug!!!
Terry

[y2kbruce]

I don't know if this is something important but I have an RCA C13-2 that tunes all the way up to 50+ MC. I think early Zenith 1000Z's could hit the 64 MC levels but later ones were de-tuned on their high end.

[Alan Douglas]

My 1937-ish Stromberg-Carlson tunes to 60mc but I'm sure the sensitivity there is zilch.

[Arran]

There was some debate about whether a brand Z 1000Z could receive up to frequencies as high as 64 MC but the general opinion was that it was highly unlikely whether they could given the front end design. Apparently the 1000Z uses a 6A7 convertor tube and pentagrid convertors tend to produce a lot of noise at higher frequencies. This is why most higher end shortwave sets from the 1930s and 40s tended to use separate mixer and oscillator tubes or duel section convertor tubes like a 6J8, 6K8, etc.
Of the two makes I would put my bets on a high end RCA being able to receive up to 50 MC, or a Philco 37-665 up to 42 MC over a brand Z set just because of the layout of the band switch and the related coils. Of course tuning up to 60 MC in the mid 1930s would be something that a 1000Z or other radio would be something that likely couldn't be confirmed or denied at the time since there likely wasn't much going on at the frequency at the time.
Regards
Arran

[Radioroslyn]

Back in the '30's 60mc was the 5 Meter ham band till after the war then hams got 50-54MC (6 mtr band) and a new thing called TV got 60MC.
Terry

[Conelrad]

Take a look here, "Ultra-High Frequency" Hi-Fi broadcast was authorized by the FRC before Armstrong's FM came into play:

http://www.theradiohistorian.org/Apex/Apex1.htm

Here is a link to discussion and photos of an APEX RCA transmitter I have today:

http://amfone.net/Amforum/index.php?topi...252158#new

73 Dennis

[wa2ise]

There's still some AM used on VHF, albeit not hi-fi. Namely the aviation band just above 108MHz.

It would be difficult or expensive to build and sell broadcast AM radios for the VHF band, the front ends would likely drift too much to stay on a 20KHz wide AM station. You see this problem on higher SW band radios trying to tune in a station around 19MHz. The radios that convert immediately from 19MHz to the 455KHz IF, the local oscillator, usually a pentagrid converter using an LC circuit drifts a lot. Oh, crystals would work better, but are too expensive. FM broadcast stations are much wider, about 200KHz, so drift is less serious to keep one station tuned in.