"David Forsyth" wrote in message
...
Would it be possible, though not necessarily practical, to make a reciever
for the modern FM broadcast band, using only pre-WWII tube technology? I
know they had FM on a lower frequency band at that time.

About half the present frequency.

What sorts of
tubes could one use from the 1930's to make a reciever that could tune in
the modern FM band?

It was something of an effort for them to reach even 50 MHz. Tubes like the
6AC7 would have some gain. No one building entertainment radios had heard
of noise figure, so their sensitivity was terrible by post-war standards.
One of the most popular and best prewar tuners was the GE JFM-90. Its front
end was two pentode mixers, one after the other. Its noise figure must have
been astronomical. At least 20 or 30 dB worse than today's radios.

I'm sure I wont actually attempt such a thing,
especially any time soon, but just wondered how difficult it might be.

The main problem would be the large cpapacitance in the big octal tubes.
IIRC, the first all-glass 7-pin miniature tubes didn't appear until 1940-41,
the 9001, 9002, and 9003. You could build a fair set with them given
today's knowledge.

Are
there any schematics or construction articles from the late 30's about
making FM radios that might be adapted over to the new FM band?

The new band wasn't chosen until about the end of WW2, so prewar sets
weren't designed with it in mind. There were only a dozen or so operating
FM stations before WW2, so there wasn't a lot of discussion of the
technology. I have/had a just-prewar book of build-it-yourself radios put
out by Popular Science (I think) which had an FM set. It was pretty
complicated. They hadn't learned how to cut corners. The IF in old-band sets
was 4.3 MHz, not today's 10.7 MHz. The lower frequency allowed better gain
with the tubes at hand, and the narrower FM band didn't result in inband
images. Modulation, etc, was the same as today.

Some of old VHF Hallicrafters sets used the acorn 954, 955, etc, tubes.
They would do ok at 100 MHz, but were exotic and never used in consumer
equipment.