FM from the stone age?
 

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

"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

In article ,
"Frank Dresser" wrote:

"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.

Different pre-emphasis is hardly a big deal, the important thing is that
the only significant difference was the frequency band used. The FM
deviation was the same for the pre war and the post war systems, so a pre
war IF strip and detector would work on the post war band, the only
potential problem being image responses due to the lower IF frequency used
pre war.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

In article ,
"Frank Dresser" wrote:

"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.

Different pre-emphasis is hardly a big deal, the important thing is that
the only significant difference was the frequency band used. The FM
deviation was the same for the pre war and the post war systems, so a pre
war IF strip and detector would work on the post war band, the only
potential problem being image responses due to the lower IF frequency used
pre war.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

R J Carpenter wrote:

"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.

Articles I have seen about early attempts at VHF talked about
removing the tube bases to reduce lead inductance but gain was still
very low, even around 50 MHz. The early, hand made tubes used widely
spaced elements that didn't perform very well at higher frequencies.
Remember the old "Let the hams have 160 meters an up because its
useless? It was, because there was nothing available at the time to make
use of higher frequencies. Remember too, that early RADAR was at lower
than optimum frequencies, as well. The 15E was an early RADAR
transmitter tube that pushed the limits of the day. If 100 MHz or high
band VHF was reasonable technology at the start of WWII you would have
seen a lot of equipment surplus for those bands, rather than the HF
band.
--


Michael A. Terrell
Central Florida

R J Carpenter wrote:

"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.

Articles I have seen about early attempts at VHF talked about
removing the tube bases to reduce lead inductance but gain was still
very low, even around 50 MHz. The early, hand made tubes used widely
spaced elements that didn't perform very well at higher frequencies.
Remember the old "Let the hams have 160 meters an up because its
useless? It was, because there was nothing available at the time to make
use of higher frequencies. Remember too, that early RADAR was at lower
than optimum frequencies, as well. The 15E was an early RADAR
transmitter tube that pushed the limits of the day. If 100 MHz or high
band VHF was reasonable technology at the start of WWII you would have
seen a lot of equipment surplus for those bands, rather than the HF
band.
--


Michael A. Terrell
Central Florida

"John Byrns" wrote in message
...

Different pre-emphasis is hardly a big deal, the important thing is
that
the only significant difference was the frequency band used. The FM
deviation was the same for the pre war and the post war systems, so a
pre
war IF strip and detector would work on the post war band, the only
potential problem being image responses due to the lower IF frequency
used
pre war.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/


Yep. But the original poster might as well take the difference into
account. Also, I think a 10.7 Mc IF strip would still be allowed under
a pre-war tube technology stipulation.

Frank Dresser

"John Byrns" wrote in message
...

Different pre-emphasis is hardly a big deal, the important thing is
that
the only significant difference was the frequency band used. The FM
deviation was the same for the pre war and the post war systems, so a
pre
war IF strip and detector would work on the post war band, the only
potential problem being image responses due to the lower IF frequency
used
pre war.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/


Yep. But the original poster might as well take the difference into
account. Also, I think a 10.7 Mc IF strip would still be allowed under
a pre-war tube technology stipulation.

Frank Dresser

As I recall, Armstrong invented and patented the FM radio before WWII.
If I'm correct, his patent should show a schematic of the circuit he
used. It's probably still available from the patent office.

Roy Lewallen, W7EL

As I recall, Armstrong invented and patented the FM radio before WWII.
If I'm correct, his patent should show a schematic of the circuit he
used. It's probably still available from the patent office.

Roy Lewallen, W7EL

"Roy Lewallen" wrote in message
...
As I recall, Armstrong invented and patented the FM radio before WWII.
If I'm correct, his patent should show a schematic of the circuit he
used. It's probably still available from the patent office.


It was actually posited in a presentation in 1935. See Wikipedia entry on
FM.

"Roy Lewallen" wrote in message
...
As I recall, Armstrong invented and patented the FM radio before WWII.
If I'm correct, his patent should show a schematic of the circuit he
used. It's probably still available from the patent office.


It was actually posited in a presentation in 1935. See Wikipedia entry on
FM.

David Forsyth wrote:

Would it be possible, though not necessarily practical, to make a receiver
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.

I have a few pre war FM sets, see
http://www.geocities.com/wa2ise/radios/fm45.html

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

Focus on the front end. Once you get to the IF, then my Emerson 460 pre
war set
would have the same technology as your "what if" set. I think acorn
tubes were pre war,
and were designed for VHF service. 2 or 3 such tubes (one RF amp,
another local
osc, and the 3rd the mixer) should make a good 100MHz front end. The
above Emerson
had an IF around 4 or was it 8 MHz, used octal tubes like 6SG7 and 6SH7
and a 6H6
for an FM detector.

David Forsyth wrote:

Would it be possible, though not necessarily practical, to make a receiver
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.

I have a few pre war FM sets, see
http://www.geocities.com/wa2ise/radios/fm45.html

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

Focus on the front end. Once you get to the IF, then my Emerson 460 pre
war set
would have the same technology as your "what if" set. I think acorn
tubes were pre war,
and were designed for VHF service. 2 or 3 such tubes (one RF amp,
another local
osc, and the 3rd the mixer) should make a good 100MHz front end. The
above Emerson
had an IF around 4 or was it 8 MHz, used octal tubes like 6SG7 and 6SH7
and a 6H6
for an FM detector.

Brenda Ann wrote:

"Roy Lewallen" wrote in message
...


As I recall, Armstrong invented and patented the FM radio before WWII.
If I'm correct, his patent should show a schematic of the circuit he
used. It's probably still available from the patent office.




It was actually posited in a presentation in 1935. See Wikipedia entry on
FM.





FM back then was on frequencies around 25MHz for experiments. Ordinary
higher frequency HF SW front ends would have sufficed, with a higher
frequency IF strip. Today hams have a
small 10 meter sub-band for FM somewhere around 29MHz. Later a
broadcast band
from about 41 to 50MHz was set up. See
http://members.aol.com/jeff560/jeff.html for more FM history.

Brenda Ann wrote:

"Roy Lewallen" wrote in message
...


As I recall, Armstrong invented and patented the FM radio before WWII.
If I'm correct, his patent should show a schematic of the circuit he
used. It's probably still available from the patent office.




It was actually posited in a presentation in 1935. See Wikipedia entry on
FM.





FM back then was on frequencies around 25MHz for experiments. Ordinary
higher frequency HF SW front ends would have sufficed, with a higher
frequency IF strip. Today hams have a
small 10 meter sub-band for FM somewhere around 29MHz. Later a
broadcast band
from about 41 to 50MHz was set up. See
http://members.aol.com/jeff560/jeff.html for more FM history.

In article , "David Forsyth"
writes:

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?

I doubt you will find much in amateur radio periodicals. They do
exist in various corporate libraries, though, since the VHF and up
radios were being pioneered in the late 1930s, some of the first being
police mobile radios. Those would evolve into the SCR-300 backpack
"walkie-talkie" of WW2 Army use and those shiny chrome button
channel select "tank radios" used mobile back then. The AN/TRC-1
through TRC-4 of WW2 times was low VHF (70 to 90 MHz) using
octal base tubes, PM with lots of multiplier stages following a MF
crystal oscillator.

Of course there are lead length problems with big bases as well as
the electrode connecting leads within bigger tube envelopes. What
most folks don't consider is the electron transit time within the tube
structure. That is slower than the speed of light (don't have an exact
value handy) and will cause a significant phase change between
grid input and plate output at VHF and above. The "lighthouse" triode
structure (ultimate may be the 2C39) has terribly short tube electrode
spacings allowing operation on up to 2.5 GHz...very quick electron
transit time internally.

Note: Klystrons and magnetrons go much higher in frequency. In the
case of the klystron, an integral tuned cavity structure is an absolute
requirement for operation. The magnetron depends upon both the
diode spacing (it is only a diode) and the magnetic field and the voltage
and the output tuned cavity structure to oscillate at X-band.

Anyone can play games with old, big tubes used at low-VHF and
arrange all kinds of neat tuned circuits to work with long leads and the
long electron transit time. Problem is, the amount of extra components
isn't really worth it. Whenever a tube has to be replaced (happened
often due to filament technology still lagging) then you would need to
do a humongous amount of retuning. About the only thing workable
for the oldie tubes is the distributed amplifier wherein LOTS of tubes
were arranged along tapped delay lines for grid inputs and plate
outputs. [the Tektronix 54x series of oscilloscopes uses such an
arrangment as the final CRT voltage driver for vertical deflection
plates] Very good as a space heater for a residence in winter...

The electron transit time thing is akin to a low f_sub_t in transistors.
Such low f_sub_t bipolars might be okay on low HF but their
characteristics don't allow good amplification or easy oscillation at
VHF and higher. Some of the newer SiGe bipolars have f_sub_ts in
the tens of GHz range.

Electron transit time depends on filament-cathode temperature, tube
geometry (and element spacings), and accelerating potential (screen
and plate quiescent voltage). There's no precise value that fits all
tubes. To view what did work at 70-90 MHz, find an old AN/TRC-1
Technical Manual and see which octal base tubes were used there.
The transmitter box final amplifier was an 829, good for about 50 W,
but not an octal base tube.

Len Anderson
retired (from regular hours) electronic engineer person
[and caretaker of TRC-1s and TRC-8s a half century ago, among
other tube-based radios]

In article , "David Forsyth"
writes:

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?

I doubt you will find much in amateur radio periodicals. They do
exist in various corporate libraries, though, since the VHF and up
radios were being pioneered in the late 1930s, some of the first being
police mobile radios. Those would evolve into the SCR-300 backpack
"walkie-talkie" of WW2 Army use and those shiny chrome button
channel select "tank radios" used mobile back then. The AN/TRC-1
through TRC-4 of WW2 times was low VHF (70 to 90 MHz) using
octal base tubes, PM with lots of multiplier stages following a MF
crystal oscillator.

Of course there are lead length problems with big bases as well as
the electrode connecting leads within bigger tube envelopes. What
most folks don't consider is the electron transit time within the tube
structure. That is slower than the speed of light (don't have an exact
value handy) and will cause a significant phase change between
grid input and plate output at VHF and above. The "lighthouse" triode
structure (ultimate may be the 2C39) has terribly short tube electrode
spacings allowing operation on up to 2.5 GHz...very quick electron
transit time internally.

Note: Klystrons and magnetrons go much higher in frequency. In the
case of the klystron, an integral tuned cavity structure is an absolute
requirement for operation. The magnetron depends upon both the
diode spacing (it is only a diode) and the magnetic field and the voltage
and the output tuned cavity structure to oscillate at X-band.

Anyone can play games with old, big tubes used at low-VHF and
arrange all kinds of neat tuned circuits to work with long leads and the
long electron transit time. Problem is, the amount of extra components
isn't really worth it. Whenever a tube has to be replaced (happened
often due to filament technology still lagging) then you would need to
do a humongous amount of retuning. About the only thing workable
for the oldie tubes is the distributed amplifier wherein LOTS of tubes
were arranged along tapped delay lines for grid inputs and plate
outputs. [the Tektronix 54x series of oscilloscopes uses such an
arrangment as the final CRT voltage driver for vertical deflection
plates] Very good as a space heater for a residence in winter...

The electron transit time thing is akin to a low f_sub_t in transistors.
Such low f_sub_t bipolars might be okay on low HF but their
characteristics don't allow good amplification or easy oscillation at
VHF and higher. Some of the newer SiGe bipolars have f_sub_ts in
the tens of GHz range.

Electron transit time depends on filament-cathode temperature, tube
geometry (and element spacings), and accelerating potential (screen
and plate quiescent voltage). There's no precise value that fits all
tubes. To view what did work at 70-90 MHz, find an old AN/TRC-1
Technical Manual and see which octal base tubes were used there.
The transmitter box final amplifier was an 829, good for about 50 W,
but not an octal base tube.

Len Anderson
retired (from regular hours) electronic engineer person
[and caretaker of TRC-1s and TRC-8s a half century ago, among
other tube-based radios]

You're going to have a bit of trouble with the older tubes. They had long
skinny leads leading down to those high-capacitance octal bases.

Hams were able to get things going up around 140Mc/s, but it was mainly
super-regen receivers.

If you want to try it, I'd find the smallest dual-triodes of that era, say
6SN7's, and make up at least one maybe two cascode Rf amplifier stages, then
another triode mixer, then maybe another cascode first IF amp. By then you
should have enough signal to start using old pentodes as IF amplifiers. If
localts are allowed, the 7F7 IIRC is probably a much lower capacitance
dual-triode.

I do recall one post-war Sparton FM set that used a 6AC7 as the RF
amplifier, a 7Q7 (loctal 6SA7) as the osc/mixer, then three 6SJ7's for IF
amplifiers and limiters. Worked surprisingly well.

You're going to have a bit of trouble with the older tubes. They had long
skinny leads leading down to those high-capacitance octal bases.

Hams were able to get things going up around 140Mc/s, but it was mainly
super-regen receivers.

If you want to try it, I'd find the smallest dual-triodes of that era, say
6SN7's, and make up at least one maybe two cascode Rf amplifier stages, then
another triode mixer, then maybe another cascode first IF amp. By then you
should have enough signal to start using old pentodes as IF amplifiers. If
localts are allowed, the 7F7 IIRC is probably a much lower capacitance
dual-triode.

I do recall one post-war Sparton FM set that used a 6AC7 as the RF
amplifier, a 7Q7 (loctal 6SA7) as the osc/mixer, then three 6SJ7's for IF
amplifiers and limiters. Worked surprisingly well.

On Thu, 13 Nov 2003 17:33:19 -0800, Roy Lewallen
wrote:

As I recall, Armstrong invented and patented the FM radio before WWII.
If I'm correct, his patent should show a schematic of the circuit he
used. It's probably still available from the patent office.

Roy Lewallen, W7EL

Roy-

Armstrong's classic paper "A Method of Reducing Disturbances in Radio
Signaling by a System of Frequency Modulation" was published in 1936
in the November Proc. IRE. (The paper was presented in a demonstration
at the Nov 1935 IRE New York meeting.)

His field work started 1934, at 44 MHz, with a 2KW 44 MHz transmitter
on the Empire State Building shortly thereafter (the article is a bit
vague on the timing of this part of his operation). (Also, the
frequency was changed to 41 MHz at some point during the trials.)

Armstrong also notes the problem with receiver RF amplifiers at this
frequency and thanks RCA for its provision of experimental VHF
receiving tubes.

His detector circuit looks like a conventional discriminator to me;
two detectors each coupled to a tuned circuit with the outputs summed.
One detector gives + and the other a - output. One tuned circuit
resonates on the high side of the IF passband the the other on the low
side. Each detector fed by an independent buffer amplifier. The
receiver was a double conversion, with the first IF at 6 MHz and the
second IF (and detection) at 400 KHz and a passband of 150 KHz.


Jack K8ZOA

On Thu, 13 Nov 2003 17:33:19 -0800, Roy Lewallen
wrote:

As I recall, Armstrong invented and patented the FM radio before WWII.
If I'm correct, his patent should show a schematic of the circuit he
used. It's probably still available from the patent office.

Roy Lewallen, W7EL

Roy-

Armstrong's classic paper "A Method of Reducing Disturbances in Radio
Signaling by a System of Frequency Modulation" was published in 1936
in the November Proc. IRE. (The paper was presented in a demonstration
at the Nov 1935 IRE New York meeting.)

His field work started 1934, at 44 MHz, with a 2KW 44 MHz transmitter
on the Empire State Building shortly thereafter (the article is a bit
vague on the timing of this part of his operation). (Also, the
frequency was changed to 41 MHz at some point during the trials.)

Armstrong also notes the problem with receiver RF amplifiers at this
frequency and thanks RCA for its provision of experimental VHF
receiving tubes.

His detector circuit looks like a conventional discriminator to me;
two detectors each coupled to a tuned circuit with the outputs summed.
One detector gives + and the other a - output. One tuned circuit
resonates on the high side of the IF passband the the other on the low
side. Each detector fed by an independent buffer amplifier. The
receiver was a double conversion, with the first IF at 6 MHz and the
second IF (and detection) at 400 KHz and a passband of 150 KHz.


Jack K8ZOA

Now waitaminnit! We have TWO Bill Turners in this mess. Do we have to play
To Tell The Truth?

"Bill Turner" wrote in message
...
On Fri, 14 Nov 2003 02:41:36 GMT, Robert Casey
wrote:

Today hams have a
small 10 meter sub-band for FM somewhere around 29MHz.

__________________________________________________ _______

That's for WIDE band FM. Narrow band FM is permitted anywhere phone is
allowed, although rarely used.

--
Bill, W6WRT

Now waitaminnit! We have TWO Bill Turners in this mess. Do we have to play
To Tell The Truth?

"Bill Turner" wrote in message
...
On Fri, 14 Nov 2003 02:41:36 GMT, Robert Casey
wrote:

Today hams have a
small 10 meter sub-band for FM somewhere around 29MHz.

__________________________________________________ _______

That's for WIDE band FM. Narrow band FM is permitted anywhere phone is
allowed, although rarely used.

--
Bill, W6WRT

The other one is WA0ABI, I believe.

"Bill Turner" wrote in message
...
On Fri, 14 Nov 2003 16:19:33 -0700, "Steven Dinius"
wrote:

Now waitaminnit! We have TWO Bill Turners in this mess. Do we have to
play
To Tell The Truth?

__________________________________________________ _______

Mom would never lie to me... would she?

--
Bill, W6WRT

The other one is WA0ABI, I believe.

"Bill Turner" wrote in message
...
On Fri, 14 Nov 2003 16:19:33 -0700, "Steven Dinius"
wrote:

Now waitaminnit! We have TWO Bill Turners in this mess. Do we have to
play
To Tell The Truth?

__________________________________________________ _______

Mom would never lie to me... would she?

--
Bill, W6WRT

Yep, he's W6 William R Turner. Congrats on snagging your vanity call.

"Steven Dinius" wrote in message
...
The other one is WA0ABI, I believe.

"Bill Turner" wrote in message
...
On Fri, 14 Nov 2003 16:19:33 -0700, "Steven Dinius"
wrote:

Now waitaminnit! We have TWO Bill Turners in this mess. Do we have to
play
To Tell The Truth?

__________________________________________________ _______

Mom would never lie to me... would she?

--
Bill, W6WRT

Yep, he's W6 William R Turner. Congrats on snagging your vanity call.

"Steven Dinius" wrote in message
...
The other one is WA0ABI, I believe.

"Bill Turner" wrote in message
...
On Fri, 14 Nov 2003 16:19:33 -0700, "Steven Dinius"
wrote:

Now waitaminnit! We have TWO Bill Turners in this mess. Do we have to
play
To Tell The Truth?

__________________________________________________ _______

Mom would never lie to me... would she?

--
Bill, W6WRT

"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. 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

"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. 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

"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. 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



The RCA 10T tombstone used the new metal tubes, and had an
UltraShortwave band that reached to over 60 mc. Unfortunately,
most of the RCAs had serious problems with the LO dropping off
at about 50 mc orso, very few of the radios ever seemed to actually
tune that high! I think I've seen one example that worked across the
full tuning range without twiddling the circuitry to make it work.
Bu, in 1936, probably no one even noticed, or cared.

Pete