the regulated voltage should be measured and adjusted as necessary,
as described in paragraph 4-6. When any tube in the regulator
cir
-
cuit is replaced,
a
check also should be made to
make certain that
the regulated voltage re mains essentially constant when the line volt
-
age is varied from 105 to 125 volts (or from 210 to 250 volts, on
230 volt operation). Since failure to regulate over this range usually
is
a
function of tubes, regulator tubes should be replaced as neces
-
sary to obtain satisfactory regulation.
If
tube V3, V4, V5, V6, or V7 is replaced, the gain of the selective
amplifier should be checked as described
in
paragraph 4-8.
4-3 REPLACEMENT OF LAMP R13
Lamp R13 has an extremely long life, theoretically almost infinite,
and should not have to be replaced. Since the lamp contrdls the
a-
mount of negative feedback in the oscillator circuit,
if
for any rea-
son the lamp should
fail,
the voltage generated at the output of tube
V2 should be measured after the replacement lamp has been in-
stalled.
Measurement and adjustment of the oscillator output are described
in paragraph 4-7.
If
the adjustment does not bring the oscillator
output voltage within the specified limits, the replacement lamp
should be rejected and another lamp installed. The test procedure
should then be repeated.
4-4 VARIABLE RESISTORS
Should any of the variable resistors require replacement, connec-
tion
should be made as shown in Fig. 7.
If
resistor R18 is replaced, the oscillator output voltage should be
measured and adjusted as described in paragraph 4-7.
If
resistor R69 in the voltmeter circuit is replaced, the procedure
for calibrating the voltmeter (see paragraph 4-10) should be per-
formed.
If
resistor R81 in the voltage regulator circuit is replaced check
the level of the regulated voltage
and adjust R8
1
as necessary, as
described in paragraph
4-6.
If
resistor R96
is replaced readjust the gain of the selective am-
plifier, as described in paragraph 4-8.
If resistor R74 is replaced, check the 600G output as described in
paragraph 4-11.
If
resistor R79
in the filament supply is replaced, readjust the
hum balance as described in paragraph 4-9.
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