On Thu, 10 Nov 2011, David Griffith wrote:

Is there such thing as a modern databook or catalog of
currently-produced vacuum tubes? I'm tinkering with the idea of making
a modern tube broadcast AM receiver that I can run all the time without
thinking "gee, I'm going to pay through the nose for more tubes when the
time comes".

Pick a popular tube and build around it.

Was it the Conar receiver that used only 6U8s? Something like that, which
of course has the advantage of not requiring a bunch of different tubes.

A double triode is bound to be easy to get still, they were so common. A
7360 was too exotic, it didn't appear in any consumer equipment (though
that sort of tube did appear in some tv sets, though I'm not sure enough
that decades later there'd be a lot of stock).

It's interesting to contrast tubes with semiconductors. With tubes, one
tried to minimize the number of active elements, since they used up so
much power (in the filament) and space. With transistors, and even more
so with ICs, each stage could have loads of active devices, it was a
different method of design, allowed because the transistors were small and
low power. So a dual triode for instance, might seem lacking, but what
could you build if you were willing to use multiple tubes per stage?

Michael VE2BVW

Michael Black wrote:
On Thu, 10 Nov 2011, David Griffith wrote:

Is there such thing as a modern databook or catalog of
currently-produced vacuum tubes? I'm tinkering with the idea of making
a modern tube broadcast AM receiver that I can run all the time without
thinking "gee, I'm going to pay through the nose for more tubes when the
time comes".

Pick a popular tube and build around it.

Was it the Conar receiver that used only 6U8s? Something like that, which
of course has the advantage of not requiring a bunch of different tubes.

A double triode is bound to be easy to get still, they were so common. A
7360 was too exotic, it didn't appear in any consumer equipment (though
that sort of tube did appear in some tv sets, though I'm not sure enough
that decades later there'd be a lot of stock).

Double triodes, particularly 12ax7, I see are currently manufactured and
easily available. Can a superheterodyne receiver be made from just
that? Anyone have any useful schematics?

--
David Griffith
--- Put my last name where it belongs

David Griffith wrote:
Michael Black wrote:
On Thu, 10 Nov 2011, David Griffith wrote:

Is there such thing as a modern databook or catalog of
currently-produced vacuum tubes? I'm tinkering with the idea of making
a modern tube broadcast AM receiver that I can run all the time without
thinking "gee, I'm going to pay through the nose for more tubes when the
time comes".

Double triodes, particularly 12ax7, I see are currently manufactured and
easily available. Can a superheterodyne receiver be made from just
that? Anyone have any useful schematics?

I think you are headed in the wrong direction. You can build a nice
superhet based on the original designs from the 40s and 50s in the RCA
tube manual. All of these tubes are still very common, not expensive,
and available as NOS.

There was a fellow, I think his name was Bob DeRocca, who published a
refined 8-tube superhet on the rar+p group. Might be able to dig up
those threads via Google Groups search. I saved the schematic but have
no idea what filename I saved it under!

-Bill

Bill M wrote:
David Griffith wrote:
Michael Black wrote:
On Thu, 10 Nov 2011, David Griffith wrote:

Is there such thing as a modern databook or catalog of
currently-produced vacuum tubes? I'm tinkering with the idea of making
a modern tube broadcast AM receiver that I can run all the time without
thinking "gee, I'm going to pay through the nose for more tubes when the
time comes".

Double triodes, particularly 12ax7, I see are currently manufactured and
easily available. Can a superheterodyne receiver be made from just
that? Anyone have any useful schematics?

I think you are headed in the wrong direction. You can build a nice
superhet based on the original designs from the 40s and 50s in the RCA
tube manual. All of these tubes are still very common, not expensive,
and available as NOS.

There was a fellow, I think his name was Bob DeRocca, who published a
refined 8-tube superhet on the rar+p group. Might be able to dig up
those threads via Google Groups search. I saved the schematic but have
no idea what filename I saved it under!

I think what I'm trying to accomplish is establishing some sort of
barrier against the inevitable day when the supply of good cheap tubes
is gone and what we're left with is mostly guitar amp tubes.

I found a Bob LeRocca on rar+p who appears to be the one you're talking
about, but I can't seem to locate any mention of an 8-tube superhet.
I'll stick my head in there and see if anyone remembers this.

Still, my question remains: can one build a decent superhet radio out of
nothing but 12ax7 dual triodes?

--
David Griffith
--- Put my last name where it belongs

On 11/12/2011 03:30 AM, David Griffith wrote:
Bill wrote:
David Griffith wrote:
Michael wrote:
On Thu, 10 Nov 2011, David Griffith wrote:

Is there such thing as a modern databook or catalog of
currently-produced vacuum tubes? I'm tinkering with the idea of making
a modern tube broadcast AM receiver that I can run all the time without
thinking "gee, I'm going to pay through the nose for more tubes when the
time comes".

Double triodes, particularly 12ax7, I see are currently manufactured and
easily available. Can a superheterodyne receiver be made from just
that? Anyone have any useful schematics?

I think you are headed in the wrong direction. You can build a nice
superhet based on the original designs from the 40s and 50s in the RCA
tube manual. All of these tubes are still very common, not expensive,
and available as NOS.

There was a fellow, I think his name was Bob DeRocca, who published a
refined 8-tube superhet on the rar+p group. Might be able to dig up
those threads via Google Groups search. I saved the schematic but have
no idea what filename I saved it under!

I think what I'm trying to accomplish is establishing some sort of
barrier against the inevitable day when the supply of good cheap tubes
is gone and what we're left with is mostly guitar amp tubes.

I found a Bob LeRocca on rar+p who appears to be the one you're talking
about, but I can't seem to locate any mention of an 8-tube superhet.
I'll stick my head in there and see if anyone remembers this.

Still, my question remains: can one build a decent superhet radio out of
nothing but 12ax7 dual triodes?

At least for the BCB yes, though the AVC control ability of the 12AX7 is
questionable. For the IF stage use both haves of the tube connected in
series with the first section as a common cathode amp and the second
section as a cathode driven amp (common grid, NOT grounded grid as the
second section grid is grounded for RF via a capacitor and is connected
via a resistor to the plate of the first section). For the converter
stage the two sections are again in series, the lower section is a
Hartley oscillator (cathode to tapped coil) and the upper section is the
mixer, grid connected via a resistor to the plate of the lower section
and cap coupled to the antenna coil. Use one section of a 12aX7 diode
connected as the detector (or as a triode infinite impedance type
detector). One or two triodes as a phase inverter driving (get this) 4
or 6 12AX7's in a zero bias class B push pull parallel amp (should be
good for a couple of watts).

On Wed, 16 Nov 2011, Kenneth Scharf wrote:


Still, my question remains: can one build a decent superhet radio out of
nothing but 12ax7 dual triodes?

At least for the BCB yes, though the AVC control ability of the 12AX7 is
questionable. For the IF stage use both haves of the tube connected in
series with the first section as a common cathode amp and the second section
as a cathode driven amp (common grid, NOT grounded grid as the second section
grid is grounded for RF via a capacitor and is connected via a resistor to
the plate of the first section). For the converter stage the two sections
are again in series, the lower section is a Hartley oscillator (cathode to
tapped coil) and the upper section is the mixer, grid connected via a
resistor to the plate of the lower section and cap coupled to the antenna
coil. Use one section of a 12aX7 diode connected as the detector (or as a
triode infinite impedance type detector). One or two triodes as a phase
inverter driving (get this) 4 or 6 12AX7's in a zero bias class B push pull
parallel amp (should be good for a couple of watts).

Don't you mean a cascode for the IF amp?

You could get fancy. A dual-triode as a balanced mixer. A similar
arrangement for the IF stages, in the IC world the differential amplifier
is pretty common, and one reason seems to be the ability to control gain.
Have a balanced mixer as the detector, and feed the "bfo" input with the
incoming signal via a limiter.

The reality is, people have pretty much followed what came before. Once
in a while someone comes along with something "radically" different and
then there's another period of following along.

So the solid stated direct conversion receiver came along (the concept
existed before solid state, but I don't think "direct conversion" was used
before that 1968 article by Hayward. So instead of building regens, direct
conversion receivers were commonplace, despite the limitations. It took
some time before someone realized a better mixer would help, endless
articles about better mixers. It took almost 20 years from that Hayward
article before someone really started building good direct conversion
receivers, Roy Llewellyn using a diode DBM but actually
terminating it properly (somehing done in VHF converters and I think by
then in ham receivers for the first mixer, but not migrated to direct
conversion receivers until about 1985 or so). Then Gary Breed extended
the concept, adding phasing (not a new concept, not even to direct
conversion receivers, but still a leap forward) followed by Rick
Campbell's various works on the subject.

Somewhere in there, superhets came back, because suddenly everyon was
writing about crystal ladder filters. They'd been around before the full
wave hit, but something happened to cause a turn. And with cheap filters,
the superhet became inexpensive again, and actually simpler than some of
those fancier direct conversion receivers (though often their
complications came in the audio section).

It's hard to stretch the limits, but somehow and sometime, it happens, and
then there's some new development, followed by it becoming the status quo,
until someone stretches things again.

Michael VE2BVW

Hey OM:

Yes you can use only 12AX7's, you might need to cascode them to reduce
the miller effect so the disadvantage would be you are going to use
twice as many tubes.
There's lots of audio circuits out there, but for RF you would have to
use a 12AT7 the input capacitance of normal 12AX7's sux big time
unless you go thru a bunch of them and find sum hot 12AX7's
In the old days we used 12AT7's in garage door opener receivers they
used the low power band in the low end of VHF before it went away.
They were made here in Detroit by VEMCO.

HF band should be no problem, see this link on miller effect of
12AX7's:

http://www.aikenamps.com/MillerCapacitance.html


Still, my question remains: can one build a decent superhet radio out of
nothing but 12ax7 dual triodes?

--
David Griffith
* --- Put my last name where it belongs

On 11/18/2011 01:13 PM, Michael Black wrote:

So the solid stated direct conversion receiver came along (the concept
existed before solid state, but I don't think "direct conversion" was
used before that 1968 article by Hayward.
Actually there WAS a direct conversion receiver in QST in the 60's that
used two 6BY7's in a balanced mixer with a B&W #350 2Q4 phase shift
network. It was actually a single sideband receiver as the detector was
an image reject mixer.



Michael VE2BVW

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