12 Volt Vacuum Tube
Mike Branca - W3IRZ
.....Seeing the recent "Regen Issue" of QRPp got me started building "Regens" again. I seem to make another
one every 6 years or so. Well I needed a break from working on the Handbook Sierra so I just built
my first FET regen and was unimpressed. Besides, regens are another excuse to use vacuum tubes so I
followed an idea that I had been kicking around for some time. The object was to make a tube project and to have it run on the 12 volt bench supply.
.....Well I had complete success. This receiver was so sensitive that 40 meter CW came booming in with
the only antenna coupling being 25 feet of wire clipped to the frame of the tuning capacitor. It
would also receive some signals with no antenna. AM SW broadcast stations were easy to copy as well
as ham and commercial SSB stations.
.....Details, if anyone is interested, are in the attached JPG file but I will give a short summary.
Since I had a lot of 6 volt tubes I decided to use two as a regen and AF amplifier. I tried a lot
of tubes but settled on the 6BA6 as the regen as it ran beautifully with 12 volts on the plate.
The AF amp ran the same with 6AG5, 6BA6, and 6AU6 so I left the 6AG5 in. The filaments were wired
in series. The trick in getting high audio from a regen is to use a lot of AF inductance in the
plate circuit. An interstage tube transformer or Hi Z choke can be used but the greatest output
that I got was from an old auto ignition coil. Tried a couple and even a mower magneto coil but a
TV flyback would not work. The RC coupled AF amp would drive old fashioned 4000 ohm phones but can
easily be coupled to an amplified speaker.
.....My construction did not use a chassis. I bolted the ARC 5 osc (BC-457) coil onto the back of the
ARC 5 (BC-457) tuning capacitor using the holes that were already there that needed tapping.(not
all of them have the holes) I put a scrap of aluminum between the two that had holes for the tubes
and plate inductor. The osc tube pointed to me and the amp tube pointed away. The mess was bolted
to a scrap of aluminum that used to be the bottom plate of a tape cartridge used for computer
backup. The ARC 5 tuning capacitor and gears pretty well shielded the hand from the tuned circuit
in front but the back was another story as the field was at least 1.5 feet as you will see. Most of
my use is with a speaker so I coupled an amplified computer speaker using a Darlington pair as an
amplified HI to LOW impedance converter.
I would rate this as a one weekend project so have fun.
Mike --... ...--
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