e. Screen Supply. Screen supply rectifier tube
of --50, --10, or --5 volts fixed bias is available
V3 (fig. 4) is a 6X4 or a 6X4W electron tube,
through corresponding settings of BIAS RANGE
switch S2. Section 1 (rear) of switch S2 con-
connected in a full-wave rectifier circuit. The
nects the proper multiplier resistor (R10, R11,
plates of tube V3 are connected to winding 15-
or R12) in series with GRID BIAS VOLTS
meter M2 for each range selected. BIAS poten-
(rear) of PLATE-SCREEN RANGE switch
tiometer R29 provides fine control of the bias
S3; the dc output voltage for the screen of tube
voltage. If required, cathode-biasing resistors
under test is taken from the common cathode.
R13 through R17 are connected into the cathode
A ripple filter, that consists of capacitors C4A
circuit of the tube under test through positions
and C4B and SCREEN potentiometer R54, is
A, B, C, D, and E of switch S2; capacitor C1
connected across the output of tube V3. Poten-
bypasses these cathode-biasing resistors.
tiometer R54 also permits adjustment of dc
screen voltage within the limits set by switch S3.
The screen voltage selected is indicated on
g. Signal Supply. Ac signal voltage winding
SCREEN VOLTS meter M6, which is connected
29-30 of transformer T2 (fig. 4) is shunted by
to the filter output through multiplier resistor
a voltage divider that consists of SIGNAL-V.R.
R56. Bleeder resistor R55 improves the voltage
potentiometer R46A and resistors R47, R49,
regulation of the screen supply.
and R50. A signal voltage of 2.5, 0.5, or 0.25
f. Bias Supply. Bias supply rectifier tube V2
volts ac, selected by GM-SIGNAL RANGE
switch S5, is provided to the tube under test.
or a 6X4W
in a full-wave rectifier circuit. In this case, how-
In positions A, B, and C of switch S5, the signal
voltage supplied is 0,25 volt; in position D, the
ever, the normally positive dc cathode of the
signal voltage is 0.5 volt; in position E, the sig-
tube is grounded, and places center tap 27 of
nal voltage is 2.5 volts; in position F, the voltage
is zero. Fine control of the signal supply voltage
at a negative potential with respect to ground.
is provided through potentiometer R46A. The
The dc bias output voltage, therefore, is taken
from center tap 27. Capacitor C3 filters the ac
correct signal voltage for the tube under test is
ripple. A bleeder and voltage divider, which con-
obtained by adjusting this control until the
sists of resistors R34, R26, R27, and R28, is con-
SIGNAL meter M4 deflects to the redline at the
nected across the output of tube V2. A choice