[Milsurplus] BC-9: Gettin' to NETTIN'!

[David Stinson]

The BC-9 is very close to QSO ready.

For this test, I'm using the link-coupled tank coil
and the Triode-Connected 6AQ5 in the RF stage.

Since the "Frequency Compensation" capacitor
C6 is directly across the 120 VDC buss, 
I removed all the bypasses on the DC-DC converters 
except for the .02 between the -120V, -40V common
point and the Negative of the 12VDC input to 
the converters.   I removed the 680 pFd I had used
to replace the open 500 pFd C6 and installed a
"correct" (for VT-1, it seems) 500 pFd silver mica.

I think this is important:  To RF-isolate C6 from
the DC-DC converter, I inserted a 3mH RF choke
in the -120 lead.  An RF Choke in the +120 lead
had no effect- only in the Minus lead.

With these changes, the TX frequency shift was
reduced from 14 KC to 7 KC.  I tacked another 
75 pFd across and the shift increased.  
Note:  Changing the C6 value moves the TX
frequency only- no effect on the RX freq.

I removed the 500 pFd C6 and replaced it 
with 270 pFd.  The shift is now down to 3 KC.
Almost useable.
When I get a chance to work on it some more,
I expect to install 150 pFd and believe the 
radio will then be netted within an acceptable range.

I believe these values will be "correct" for
the 6AQ5 and tank.  It would be different for
the 01A and loop, I think.

Why does it work?  I don't know.  But the 
RF path is along the 120V minus lead, somehow.

Hope to get some more "play radio" time in 
the near future to tweak this some more.

TNX OM DE Dave AB5S