[Boatanchors] BC-9: A 96-Year-Old Veteran Wakes Up

[David Stinson]

Many thanks to all who provided info to help with
the BC-9 revival.  There did turn-out to be a couple 
of bad caps, which I disconnected and bypassed
with good ones.   The RF stage plate load resistor
had drifted up from 100K to 170K.  Paralleled another
resistor across it which brought the value back down
to 100K.  As with most "Boatanchors," there were
problems with Hi-Z grounds and a couple of 
ancient solder joints that had gone "cold."

Regeneration in the RF stage is controlled by varying
the bias to the tube.  For some reason, all the resistors
in the bias divider including the giant wire-wound pot
were burned open.  Two resistors were made of 
scramble-wound resistance wire on a bakelite or 
hard-rubber spool, covered with dimpled tar paper.
The paper was loose so I removed it to look at the
windings.  The open spot was not visible on either
and I didn't want to destroy them, so I put the paper
back on with a drop of glue and bypassed them 
with a modern replacement.
https://goo.gl/photos/Bofb6AZ4sGQzLbsy7

Getting at the giant bias pot required removing the
main chassis from the front panel assembly.
https://goo.gl/photos/7RHrGWAr9GUWtPvt8
The Almighty was kinder than I deserve, because
the open spot was right at one of the connection 
terminals.  
https://goo.gl/photos/LcC96UkJgJnGm8At6
Burnished the contacts, re-tensioned
the sliding contact and it was back in business.

The BC-9 used three Western Electric VT-1
triodes and one had to "cherry pick" from a larger
lot to get one that would operate reliably as the
Oscillator/Regenerative Detector.  Well, buying
three tested VT-1s is just a little bit "pricey."
Like, oh, $2100 worth of  "pricey." 
Not this lifetime.  So workable and hopefully 
"period" substitutes were needed.  With a small
adjustment of filament voltage, 01A tubes work 
well in Audio stages, but just don't have the 
gain to oscillate reliably in the RF stage.
With a small adjustment downward of the 
Plate Load resistor and an adaptor (Ben Hall,
you recognize this invaluable adaptor tool?),
a triode-connected 6AQ5 works.
https://goo.gl/photos/8Na94g3V8gSBCqX87

"First Light:"
Time to light-up this 96-year-old radio and see
 if it will play.
Cobbled-together four DC-DC converters to 
provide 6, 40 and 120 Volts.  Bias is provided
by two 9V batteries.   DC converters, unbypassed
and unshielded, throw a few strong spurs but 
this is just for testing.  
For the loop, used a length of RG-8.

Since my bench is in the tin-covered barn, not
much signal gets in there.  So loosely-coupled 
an external antenna to the loop.  Would have 
preferred to find a shortwave station playing 
"Over There," but 80 Meter CW was plenty cool.
https://goo.gl/photos/WLcCF1oPGc64c4Zu6

There is much left to do- need to fabricate a real
loop, build a "clean" supply and tweek the Plate
Load resistor to optimize while seeking a better
substitute tube for the RF stage.  Will also eventually
clean and repaint the cabinet, recreating the 
3rd Battalion 12th Infantry markings.  I found 
good, original paint under the case hardware and
got Sherwin Williams to match it for me in oil-base.
WWI "Olive Drab" is a darker shade than that
used in WWII- has more brown or yellow.

Lots more to do, but we're "on the way."

GL OM ES 73 DE Dave AB5S