[Milsurplus] BC-9: Answer One Question, Get Another.

[David Stinson]

Good morning, Mike.

Using an external receiver and frequency counter 
to measure the shift.
Currently, with C6 at 270 pFd, listening at, say, 
3520 KC and I close the key, the rig will transmit 
a carrier at 3517 KC and remain there- 
with surprising stability- until key-up, 
when it will return to receiving at 3520 KC.
The value of C6 varies that transmit offset.
It has no effect on receiving frequency.

There seems to be a "saturation point" for the
C6 value, above which it has no further effect-
i.e. the big bypass I had there pulled the TX freq 
off 12-14 KC depending on antenna configuration
 and loading, etc. but, curiously, that "saturated"
shift remained fairly constant between tubes.
Adding any more to C6 created no further shift.
I suppose that, once one adds .02 uFd to the 
cathode circuit of an oscillator, differences of
a few pFd tube-to-tube are insignificant.

When I get time, I'm going to try a few other
tubes that will work in transmit mode at least
and see if the "critical value" for C6 shifts with
differences in tubes.  I'm almost certain that 
would be the case but the test is needed anyway-
assumptions get me in trouble all the time, LOL.

Installing a compression trimmer may be a 
bit "tricky," given the available room.  It would 
certainly fit if I removed the large dead C6,
but I don't want to remove parts from this rig.
There's always a "work around" when one is
willing to seek it.  Hoping to find two "critical
values-"  One for using the tank-and-link 
and one for using the loop.  We'll see.

Important Aside:  
While working with the rig, a few parts that 
appeared "dead" at first look were actually
open-circuited due to contact oxidation 
(some get contact through screw mounts
rather than solder joints).  For instance, the
two 5 KOhm Grid Bias divider resistors
were not open.  Their connections were
oxidized.

When I begin a new "boatanchor" project, 
the very first step is, of course, inspection, 
cleaning and lubrication. 
The next is an inch-by-inch search for
bad solder joints and Hi-Z grounds.
It is tedious but pays big dividends. 
The key to recovery of several rigs has been 
 repair of bad grounding.  I need to add 
any other type of mechanical connection 
point to that routine.

73 Dave AB5S.