1.
With the generator set to deliver 1,000 cycles, connect a high-
impedance vacuum tube voltmeter to pin 4 of tube V3, and
measure the input to the selective amplifier.
2.
Connect the voltmeter to pin
8
of tube V5, and measure the
amplifier output. The gain through the amplifier should be
approximately 24 db
(+.
5
db).
3.
If
amplifier gain is too low or too high, adjust variable resistor
R96 (Fig. 4) to obtain approximately a 24 db gain.
NOTE
If
with
a
gain of 24 db the waveform at
the OUTPUT terminals shows clipping,
lower the gain of the amplifier until clip-
ping stops.
ADJUSTMENT OF HUM BALANCE
Variable resistor R79 (Fig. 4) provides an adjustment for mini-
mizing the beat between the oscillator and the power supply fre
-
quency. Either of two methods may be used for the adjustment.
1.
If
a
distortion analyzer such as
a
Hewlett-Packard Model 330B
or 330C is available, adjust resistor R79 for minimum distor-
tion in the output waveform with the instrument generating
5
to
20 cycles above or below the power line frequency.
2.
If
a distortion analyzer is not available, output amplitude vari-
ation (60-cycle beat) may be observed on a sensitive
high-im-
pedance vacuum tube voltmeter, and resistor R79 adjusted for
minimum variation in output amplitude with the instrument
tuned to a frequency near that of the power line. For example,
where the power line frequency is 60 cycles, the Model 206A
should be tuned with the FREQUENCY dial for maximum beat
(approximately
58
cycles),
and then resistor R79 should be
adjusted for minimum beat.
4-10 CALIBRATION OF VOLTMETER
Calibration of the control panel voltmeter is set at the factory, and
unless one of the crystal diodes in the rectifier circuit requires re-
placement or the voltmeter should be smashed, it is unlikely that
the voltmeter will require recalibration during the life of the Model
206A. To recalibrate the voltmeter, a comparison meter standard-
ized for 4 volts at 100 cycles is required.
To Next Page
Loading...
