Circuit Description— Type M
to the emitter circuits of Q6364 and Q6350.) The + 50 volts
goes to the plate circuit of V5323 (four channels) and the
+69 volts goes to the plate circuit of V5364 and V5374.
The series-connected heaters of the tubes do not supply
any current for the +50- and +69-volt sources; they simply
act as a low-impedance divider to "fix" the voltages. Cur
rent (15 ma) is supplied to the +38-volt source (S/N 101-824),
however. This current is conveniently obtained by the dif
ference in heater current drawn by the Nuvistors (135 ma)
and the current drawn by the remaining tubes (150ma).
The series-connected heaters result in a total drop of
about 61 volts. This drop, subtracted from the +75-volt
source, leaves approximately 14 volts where it is applied
across D5392 and D5390 (D5390 S/N 101-3479). The Zener
diodes clamp the voltage to 13.6 volts, ± 2 % (12.6 volts,
± 5 % — S/N 101-3479).
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