Section V
Paragraphs 5-23 to 5-29
5-24. CHASSIS HELIX CONTROL.
5-25. The chassis Helix control, R25, determines
the range of the front panel HELIX control by govern-
ing the output voltage of the regulated power supply.
This adjustment should be performed whenever a new
twt capsule is installed or the gain of the amplifier is
less than 30 db.
To adjust, proceed as follows:
a. Remove the cabinet, see paragraph 5-8.
b. Set twt HELIX control to position 5, and adjust
GRID BIAS control to obtain normal cathode current.
c. Connect a test setup as shown in figure 5-4.
d. Set the generator for the Model 492A to 4 gc,
for the Model 494A to 7 gc. For both models set the
generator attenuator to -30 dbm, in cw operation.
e. Adjust the chassis Helix control, R25, for maxi-
mum gain, as read on the 430C.
f. Change the frequency of the generator, for the
Model 492A to 8 gc, for the Model 494A to 12.4 gc,
maintaining the same power level.
g. The 430C should read greater than 0 dbm.
If
the 430C doesn't read greater than 0 dbm, readjust
the chassis Helix control, R25, to obtain from 0 dbm
to +2 dbm.
Recheck the gain for the Model 492A at
4 gc, for the Model 494A at 7 gc, and readjust R25,
if necessary, to obtain nearly equal gain at both fre-
quencies.
5-26. ANODE VOLT AGE CO TROL.
5-27. The Anode control, R30, on the chassis of the
instrument, (see figure 5-1), is provided so that the
two cathode current can be maintained at its normal
level (as indicated on the plate attached to the meter
face) as the tube ages. To adjust proceed as follows:
a. Place meter selector switch to CATH. position
and GRID BIAS control to O.
b. Rotate Anode control adjust, R30, to obtain
normal cathode current.
Also note that other tube-
element currents do not exceed their safe maximum
limits (see table 3-1).
5-28. REGULATED POWER SUPPL Y.
5-29. To check the regulated power supply, proceed
as follows:
a. Set GRID BIAS control to O.
b. Connect a dc voltmeter to the output of the
power supply, at pin 3 of VI.
c. Adjust the line voltage from low to high line
(103 - 127 volts).
Power supply voltage should not
change more than 10 volts.
5-5