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1.
Remove the bottom cover from the P.A.
tank.
2.
Loosen the locking nuts on the rear of the
neutralizing capacitors slightly,
so the shaft
will turn free with a slight drag on the shaft.
3.
Remove on
of the plate caps from the high voltage
rectifier.
4.
Replace the bottom cover on the amplifier tank.
5.
Apply low plate voltage and adjust either C303
or C308 in one direction and again check for
neutralization.
6.
If improvement results,
adjust the other capacitors
the same amount in the same direction and a„ain
recheck for neutralization.
7.
Continue this procedure step by step rotating
capacitor C303 and C308 in the direction that indi-
cates proper neutralization.
8.
Replace cap on high voltage rectifier for normal
operation and recheck neutralization.
9.
Remove the bottom cover of the amplifier tank and
retighten the locking nuts on the rear of the
neutralizing capacitors, being careful not to
move the adjustment when these locknuts are
retightened.
AMPLIFIER
The amplifier also must be neutralized for proper operation.
Improper neutralization is indicated by possible self- oscilla-
tion and great fluctuations of grid current as the plate tuning
and loading controls are adjusted through plate resonance.
To eliminate this condition:
1.
Remove amplifier tubes from their sockets.
2.
Loosen hardware securing neutralizing capacitor
plates C624 and C625,
and move capacitor plates
simultaneously either toward the tube or away from
the tube.
3.
Secure hardware,
install tube,
and turn on driver
but do not apply plate voltage.
4.
Tune grid circuit to resonance.
5.
Tune plato circuit through resonance and watch
for abnormal reflections into the grid circuit.
6.
Repeat the previous
5
steps until minimum inter-
action and grid current fluctuations occur.
Another possible method of neutralizing is to couple a sensi-
tive R.F.
metering device into the Amplifier Transmission line
output.
This can be done in the following eteps:
1.
Couple the RF device into the transmission line.
2.
Turn on the low voltage filaments and apply grid drive
but do not apply plate voltage.
6/22/61
-14-
FM- 20B
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