affected by line voltage. For resistance tests,
88. Voltage and Resistance Measurements
disconnect the power cord from the ac line and
Follow the voltage and resistance charts (figs.
remove the tubes, Make all tests from the bottom
of the chassis.
readings with the meter connected between the
a. The following circuits are affected by higher
chassis and the indicated socket lug or the com-
or lower line voltages within normal limits: fila-
ponent lug. Make all voltage tests with the tubes
ments; unregulated B+; V14 stage when selector
in place, the power switch at the ON position and,
switch S1 is at RECORD DIRECT: regulator
unless otherwise noted on the chart, with an input
stages V7, V8, V9, and V21; start motor; start
signal sufficient to cause a reading of +2 on the
coil; and motor amplifier stages V4, V5, and V6.
DB METER. For dc voltage measurements, use
b. The motor amplifier is self-regulating, so
a voltmeter with a sensitivity of 1,000 ohms per
that the motor current varies very little over a
volt, and for ac signal measurements, use a vacu-
wide range of line voltages. The effect of the line
um-tube voltmeter, unless otherwise specified.
voltage on this circuit is complex; in some cases,
Line voltage should be 115 volts ac; if it is higher
the motor current or voltage increases as the line
voltage decreases.
or lower, make allowances in measuring voltages
