Scott Dorsey wrote:
Ed wrote:

Looking for a nice superhet Rx design for 75M/40M, using 12V fil. &
plate tubes. Not needing anything fancy, schematic and any addional info
appreciated, if anyone can point me to this. Thanks.


My suggestion is that you get out the Sam's Photofacts book on car radios
and look at some of the vibrator-free tube car radio designs. It should
not be too hard to change the loopstick and/or tuning cap for 75M and 40M.

The problem you'll have is that the IF is wide as hell, but that's part
of the fun. Be sure to add a BFO!
--scott

12V plate tubes are rather rare, perform poorly compared to most anything else.
They are very low power, low gain, and low frequency. Typical amplification
factor is 10 or less. With the exception of the R392, which used 28V tubes,
and some automobile radios from the late '50s to early '60s, I don't recall that
they were used for much of anything... which is why they are rare.

There were a whole pile of different types made, pentagrid converters, sharp and
remote cutoff pentodes, triodes with diodes, pentodes with diodes, twin triodes,
.... the most amusing thing was the "power" tubes that had maximum output ratings
of 20mw!

The typical automobile radio used the following tube lineup:

RF: 12AF6 - Sharp cutoff pentode
Mixer: 12AD6 - Pentagrid converter
IF: 12AF6 - Sharp cutoff pentode
Det/AGC/1st audio: 12AE6 or 12AJ6 - medium mu triode/ twin diode
Audio amp: DS-501 Delco Germanium PNP transistor.

In a car radio, the RF/Mix/LO was tuned by a very fancy rig that moved the
slugs in the coils. The IF was 256KHz, with a 4KHz bandwidth...Real Hi-Fi!

Somewhere in my archives I have a Sams Photofact for the 12V tube radio that
is in my '60 'vette. By 1960, all transistor car radios were already
on the scene in Corvettes and Cadillacs.

In the R392, the 28V tubes in the RF section are generally bad, and kill
the sensitivity of the radio above 14MHz.

Is there a particular reason that you want to use this style of tube?

Today it is trivial to make a simple switching power supply that can provide
a couple of hundred volts at 98% efficiency, why not make one of them, and
use some real tubes?

-Chuck