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).