[Drake] R-4C BFO leakage & sensitivity

[John B. Curtis]

Hello!

1.  I have a R-4C, 26K s/n, that now shows S-meter deflection when tuning 
through the center of the passband.  The deflection is two S-units w/ the 
500 Hz filter and seven S-units with the 250Hz filter. (There is minimal 
deflection with the 1.5kc or SSB filter). There are multiple peaks in a 
very small movement of the Passband control at the center position.  There 
is no audio, just the S-meter deflection.  This seems to be no effect on 
received signals.

When the bottom cover is removed, there is no deflection (!)  If I place 
the rig on a metal pie sheet (bottom cover removed), the deflection 
returns.  Apparently something is interacting with the shielding effect of 
the metal...

I followed some old notes on this problem, identified as BFO leakage, in 
early R-4C's (mine is quite late)...all tube shields are in place and I had 
not disturbed the wiring harness.  I did not try placing a 47K resistor 
from Q5 base to ground, however.

2.  I am unable to peak the Preselector when connected to a dummy or 
non-resonant antenna The receiver seems to have plenty of sensitivity, the 
calibrator is S9 or better on all bands, and the Preselector peaks just 
fine with a resonant antenna.  A new RF amplifier tube did not make any 
difference.  This peaking criterion as a check on receive sensitivity is 
from the same notes on care & feeding of Drake's, by VE3ERP I believe.

Any thoughts on the above two problems (or non-problems) would be appreciated!

73,

John,  W0CAR


John B. Curtis
Associate Professor & Director, Petroleum Exploration and Production Center/
Potential Gas Agency
Dept. of Geology and Geological Engineering, Colorado School of Mines
Golden, CO  80401  USA
Telephone: (303) 273-3887  FAX: 303) 273-3574  jbcurtis@mines.edu
http://www.mines.edu/academic/geology/faculty/jbcurtis/