Hammarlund FM50A - Neutralization Instructions

PARTS LIST SUPPLEMENT & ERRATA SHEET
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Description
Part No.
C158
Capacitor Var. N500, 7-45 MMF, 500V.
K23059-3
C212
Capacitor, Silver Mica, 250 MMF, 350V
K23028-1
C2I3 Capacitor, Silver Mica, 250 MMF, 350Y.
K23028-1
C214
Capacitor, Disc Ceramic, .01 MFD, GMV,
1000V. M23034-8
R193
Resistor, Fixed 1K, 1/2 w. .i 10 %
K19309-49
NOTE: POSITION OF MOUND
OF SOLDER ON ROTOR
AND STATOR
NEUTRALIZATION INSTRUCTIONS
A
variable 7-45 micro microfarad capacitor, C158 has been added from
the screen grid, pin 3, of the radio frequency power amplifier, VllO
(6146) to ground.
All units are shipped from the factory with this capacitor set at the correct
point for optimum performance and under normal circumstances it need not be
changed in the field unless the power amplifier tube VI10 is changed or the
transmitter is retuned to a different frequency.
The correct neutralization adjustment procedure is as follows:
a) Set C158 for minimum capacity as shown in the above sketch. (Solder
mound of rotor furthest position away from stator).
b) Tune transmitter for maximum grid drive and maximum power output.
c) Increase capacity of C158 by turning rotor either clockwise or counter-
clockwise (solder mounds become closer) while observing plate current or final
radio frequency stage. A point will be reached where plate current is lowest and
then rises as capacity is further increased. Set neutralization capacitor C158 at
lowest plate current point followed by re-tuning of the grid, plate and antenna
loading adjustment of the final stage. Several adjustment cycles will be required
for highest power output consistent with lowest plate current.
d) Check for self oscillation by momentarily removing grid drive (remove
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