Simpson 1000 - Bias Control

THEORY OF OPERATION
applied across the primary windings. The LINE ADJUST-
MENT control drops the excess line voltage to permit ex-
actly 100 volts to be applied across the transformer.
When the control is properly adjusted, the meter will in-
dicate at the ADJ. LINE mark on the dial. The meter cir-
cuit is arranged and calibrated as an A.C. voltmeter, and
measures the voltage output of the 25 volt tap on the fila-
ment secondary of the power transformer. There is a slide
switch which is actuated at the full counterclockwise
position of the LINE ADJUSTMENT control. When the con-
trol knob is set fully counter-clockwise, the switch is open
and the instrument is turned off. Clockwise rotation will
close the switch and turn the instrument on.
BIAS CONTROL
The BIAS control in the lower left hand corner of the front
panel is a continuously variable potentiometer with a snap
switch actuated in its counterclockwise position. The
switch opens or closes a short around a 400 ohm current
limiting resistor which is used when testing high current
rectifiers.
The switch action requires the first seven divisions of
knob rotation. The switch shorts across the resistor when
the BIAS control is set at or above 7 divisions. When the
knob is set at 0, the switch is open. The rest of the po-
sitions indicate the relative value of bias voltage which is
tapped for each tube application when there is a control
grid in the tube.
The bias voltage at 7 divisions is zero, and the bias volt-
age at full clockwise rotation can be 5, 15, or 45 volts.
29