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. What sorts of
tubes could one use from the 1930's to make a reciever that could tune in
the modern FM band? I'm sure I wont actually attempt such a thing,
especially any time soon, but just wondered how difficult it might be. 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?

just curious,

Dave

There is no problem doing that. Realize that the 'modern' miniature tubes
of the 1950s that were used to make FM tuners are internally identical to
the old tubes from the 1930s.

You use a 6K7 instead of a 6SG7 for instance. Or if you want to go even
older, a 36 I think. A 27 instead of a 6AT6 (triode section).

The lead lengths are longer and might require a bit more care in layout but
it should be okay. Just look at the Hallicrafters S-27 for some ideas.

Bob

There is no problem doing that. Realize that the 'modern' miniature tubes
of the 1950s that were used to make FM tuners are internally identical to
the old tubes from the 1930s.

You use a 6K7 instead of a 6SG7 for instance. Or if you want to go even
older, a 36 I think. A 27 instead of a 6AT6 (triode section).

The lead lengths are longer and might require a bit more care in layout but
it should be okay. Just look at the Hallicrafters S-27 for some ideas.

Bob

To my simple mind, the technology is essentially the same between prewar FM
and "new" FM. You would change some coils & whatnot, primarily in the front
end (experts, chime in here as usual to correct my habitual blunders :-), to
receive and decode the same kind of signal, only in a different frequency
band. You would also want a dipole antenna of slightly different size than
what's used now. Otherwise, I see nothing to prevent you from building a
"new FM" receiver using prewar components.

Phil

To my simple mind, the technology is essentially the same between prewar FM
and "new" FM. You would change some coils & whatnot, primarily in the front
end (experts, chime in here as usual to correct my habitual blunders :-), to
receive and decode the same kind of signal, only in a different frequency
band. You would also want a dipole antenna of slightly different size than
what's used now. Otherwise, I see nothing to prevent you from building a
"new FM" receiver using prewar components.

Phil

"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.

"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.

So basically if I could somehow use 30's tubes to tune to 100 MHz more or
less, all I would need to do then is to add a suitable FM detector and
bingo? Hmm I think I will need to do a lot more research on this one....


Dave



"John H. Smith" wrote in message
...
Subject: FM from the stone age?
From: "David Forsyth"
Date: 11/13/2003 3:56 PM Central Standard Time
Message-id:

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. What sorts of
tubes could one use from the 1930's to make a reciever that could tune in
the modern FM band? I'm sure I wont actually attempt such a thing,
especially any time soon, but just wondered how difficult it might be.
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?

just curious,

Dave

Look up some ham / swl construction articles from the 30's. The "5
Meter"
ham band was quite popular among home constructors and magazine authors.
Only
very slight modifications are needed to cover the modern FM band with
these
circuits, some of which used the newest tubes out at the time, but many of
which used what would have been cheap surplus tubes from the late 20's,
early
30's.
Keep in mind that the Super- regenerative circuits you will find are
very
effective radiators of RF when they are receiving, so be careful about
slipping
into the aircraft band or bothering the neighbors. A short antenna is a
1/4
wave at these frequencies, so you can really "get out" with one of these.
Look
at the tranciever circuits, there isn't much difference between the
receive and
the transmit circuit, since a SPDT switch often was all the switching
rerquired! These will detect FM about as well as AM.
If you go with a TRF or superhet design, you'll need to add an FM
detector
of some sort or modify the AM detector a bit for slope detection. You can
see
examples of slope detectors and simple FM detectors in early broadcast FM
radios and in ham gear for 2 meters from the 30's.
There were many tricks for making early tubes work at higher
frequencies,
and the ham's articles detail them nicely. An advantage of articles from
the
30's is that they tended to lean heavily on household items, hand made
items
and surplus components due to the Depression. This makes recreating them
somewhat easier.
The reprints of Gernsback's "Official Short Wave Manual" of 1934 and
1935
are loaded with 5 meter circuits for home construction articles and
commercial
products. These are available from Lindsay and others. Old ARRL manuals
are
plentiful on Ebay or if you request one here, someone will ususally have
one to
sell reasonably.
Another source of early FM info is in the schematics of early TV
sets. The
kit sets especially, shaved tube and part counts as much as possible and
had
simple FM detectors for the FM audio.
Hams were quite active on the 5 meter band while they had it, going
by the
results, they made the available tubes work fairly well.
Neutrodyne

So basically if I could somehow use 30's tubes to tune to 100 MHz more or
less, all I would need to do then is to add a suitable FM detector and
bingo? Hmm I think I will need to do a lot more research on this one....


Dave



"John H. Smith" wrote in message
...
Subject: FM from the stone age?
From: "David Forsyth"
Date: 11/13/2003 3:56 PM Central Standard Time
Message-id:

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. What sorts of
tubes could one use from the 1930's to make a reciever that could tune in
the modern FM band? I'm sure I wont actually attempt such a thing,
especially any time soon, but just wondered how difficult it might be.
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?

just curious,

Dave

Look up some ham / swl construction articles from the 30's. The "5
Meter"
ham band was quite popular among home constructors and magazine authors.
Only
very slight modifications are needed to cover the modern FM band with
these
circuits, some of which used the newest tubes out at the time, but many of
which used what would have been cheap surplus tubes from the late 20's,
early
30's.
Keep in mind that the Super- regenerative circuits you will find are
very
effective radiators of RF when they are receiving, so be careful about
slipping
into the aircraft band or bothering the neighbors. A short antenna is a
1/4
wave at these frequencies, so you can really "get out" with one of these.
Look
at the tranciever circuits, there isn't much difference between the
receive and
the transmit circuit, since a SPDT switch often was all the switching
rerquired! These will detect FM about as well as AM.
If you go with a TRF or superhet design, you'll need to add an FM
detector
of some sort or modify the AM detector a bit for slope detection. You can
see
examples of slope detectors and simple FM detectors in early broadcast FM
radios and in ham gear for 2 meters from the 30's.
There were many tricks for making early tubes work at higher
frequencies,
and the ham's articles detail them nicely. An advantage of articles from
the
30's is that they tended to lean heavily on household items, hand made
items
and surplus components due to the Depression. This makes recreating them
somewhat easier.
The reprints of Gernsback's "Official Short Wave Manual" of 1934 and
1935
are loaded with 5 meter circuits for home construction articles and
commercial
products. These are available from Lindsay and others. Old ARRL manuals
are
plentiful on Ebay or if you request one here, someone will ususally have
one to
sell reasonably.
Another source of early FM info is in the schematics of early TV
sets. The
kit sets especially, shaved tube and part counts as much as possible and
had
simple FM detectors for the FM audio.
Hams were quite active on the 5 meter band while they had it, going
by the
results, they made the available tubes work fairly well.
Neutrodyne

"David Forsyth" wrote in message
...
So basically if I could somehow use 30's tubes to tune to 100 MHz more
or
less, all I would need to do then is to add a suitable FM detector and
bingo? Hmm I think I will need to do a lot more research on this
one....


Dave



You should be able to get good performance with acorn tubes in the front
end. Acorn tubes pre-date octals, if I recall.

The prewar FM setup not only used a different band, but also a different
audio pre-emphesis. 100us as compared to the current 75us.

Frank Dresser