[Milsurplus] Low B+: The Genius of A.R.C.

[Mike Morrow]

> The equipment is not for a "space probe"...

But what about "space charge"? :-)

The performance of those low screen/plate voltage tubes, which rely
on the space charge around the cathode, suffer greatly if the
*filament* voltage is low.  I suspect that conventional tubes at low
B+ would likewise see some improved performance if the filament supply
was near the high end of the permissible range.

There's some interesting info about the 12 vdc tubes that saw so much
use in car radios in the late 1950s through the mid-1960s at:

  http://www.junkbox.com/electronics/lowvoltagetubes.shtml

When I was 14, I bought several such radios for a dollar from a local
car junkyard.  They had Conelrad station markings.  All the car radios
had an RF stage ahead of the mixer.  That helped reduce the Morse images
that came in from strong coastal station signals in the 420 to 520 kHz
MF maritime band.  (I used a BC-453-A to copy those stations.)  With a
short wire antenna, they made top-performing AM BCB sets, compared to
almost any in-house AM BCB radio that could be purchased.  Because the
input connection could be shielded, I built single-band converters for
some of the shortwave BC bands to use with the in-house car radio.  (My
Dad's Drake 2-A was ham bands only.)  All this was in 1966.  I've still
got those car radios...but I think I scrapped the SW BCB converters after
I got a R-105/ARR-15 through Navy MARS in 1969.

Mike / KK5F