just the gain of the rf amplifier, proceed
volts 10 percent, 50-1,000 cycles)
as follows:
depending on whether power trans-
(1) C o n n e c t the output terminals of
former T1 is connected for 115-
the test oscillator to the INPUT
or 230-volt operation.
(2) C o n n e c t the multimeter between
terminals of the rf amplifier (fig.
pin 3 of V5 and chassis ground, and
apply power to the rf amplifier.
terminal on the test oscillator con-
(3) The regulated output voltage should
nects to the G terminal on the rf
measure between +205 and +215
amplifier.
volts dc.
(2) C o n n e c t the OUTPUT terminals
(4) If the regulated output voltage is
of the rf amplifier to the INPUT
not between +205 and +215 volts,
terminals of the vtvm.
remove resistor R25 and substi-
(3) Set the test oscillator controls to
tute another resistor with the
produce a 1,000-cycle signal at a
proper value necessary to produce
level of 0.1-volt root mean square
the correct regulated output volt-
(rms).
age. T h i s new resistor is still
(4) Set the GAIN switch to 40 DB and
referred to as R25.
apply power to the rf amplifier.
b. Filament Voltage. Whenever seleni-
(5) A d j u s t R6 to produce exactly a
10-volt rms (40-db gain) indica-
u m rectifier CR1 or electron tubes V1
tion on the vtvm.
and V2 are replaced, check the +6.3 fila-
(6) Set the GAIN switch to 20 DB. The
ment voltage as follows:
vtvm should indicate 1-volt rms
(1) Connect the rf amplifier to a suit-
(20-db gain).
able power source (e(1) above).
(7) If the indication is slightly above
(2) Connect the multimeter between
or below 1-volt rms, adjust R6 to
pin 4 of V1 and V2 and chassis
bring the vtvm meter needle half-
ground.
w a y back to the 1-volt mark.
(3) Apply power to the rf amplifier.
(8) The gain of the rf amplifier in now
(4) The filament voltage should meas-
set to produce either a gain of 40
ure +6.3 volts.
db 0.13 or 20 db 0.13.
Note. Make this measurement with
(9) If adjustment of R6 cannot bring
V1 and V2 both in their sockets for a
the gain within the above toler-
proper reading.
ances, check resistor R3A and re-
(5) If the filament voltage is not +6.3
place, if defective. Repeat the gain
vols, adjust variable resistor R27
adjustment procedure.
t o produce the correct filament
Note. Reduction of the value of R3A
voltage.
will increase the gain of the rf ampli-
fier when the GAIN sw itch is set for
20 DB operation.
14. RF Amplifier Gain Adjustment
15. Frequency Response Adjustment
a. General. The rf amplifier amplifies
an input signal by either 20 db or 40 db.
the rf amplifier is adjusted by variable
depending on the setting of GAIN switch
capacitor C11 which is located on the top
S1 and the setting of gain adjust resistor
of the chassis (fig. 6). The frequency re-
R6. The GAIN switch requires no adjust-
sponse of the rf amplifier when set for a
ment. Resistor R6, however, controls the
40 DB gain must be flat within 0.5 db be-
amount of feedback to V1 and must be
tween 10 cycles per second (cps) and 1
properly set in conjunction with the GAIN
mc, and within +1 db between 5 cps and 2
switch to produce a fixed gain of 20 db or
mc. The frequency response of the rf am-
40 db.
b. Gain Adjustment Procedure. To ad-
plifier when set for a 20 DB gain must be
15
