eXact 100 - Page 15

decreases the resultant rise in screen volt-
age is coupled to the grid of V53 causing
it to go into conduction. The corresponding
drop in plate voltage is coupled back to
the grid of V5}. The biases are adjusted
such that when V53 is conducting full, V5)
is cut-off. This stable state is maintained
until the next negative trigger arrives
from V52 causing the action to reverse and
the multi to return to its original quies-
cent state. SINCE ONLY THE NEGATIVE SPIKES
FROM THE TRIGGER GENERATOR V51 SWITCH THE
MULTIVIBRATOR, A 1KC SQUARE WAVE IS GENER-
ATED WHOSE SYMMETRY IS LIMITED ONLY BY THE
FREQUENCY STABILITY OF У51 (about one part
in ten thousand).
MAX. OUTPUT ADJ.
R67 sets the maximum voltage to which the
plate of V54 can rise.
The VARIABLE control R68 is a mechanical-
ly linked dual COARSE-FINE potentiometer
which sets the positive voltage level at
the plate of V5h.
In the DC position of the OUTPUT switch,
the multivibrator is rendered inoperative
by disconnecting the cathode of 951. Plate
voltage of V54 rises to whatever level is
selected by the VARIABLE control.
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