Figure 43. Multivibrator and motor amplifier driver Facsimile Transceiver TT-1F/TXC-1.
through the contacts of STANDBY-
is common to both circuits. The motor
current is a series of dc pulses that reoccur
MON-TALK switch S5 and selector
1,800 times per second, since tubes V5 and
switch S1 when both are operated to
the STANDBY positions.
V6 conduct only on the positive half-
cycles of the 1,800-cycle input wave.
46). In unmodified Facsimile Transceivers TT-1/
Choke T6 is not a part of the series-
TXC-1 and TT-1A/TXC-1 (fig. 44), V5 and V6
resonant circuit; its ac impedance is high
are type 6AC5GT/G tubes (type 1635 tubes when
and it may be considered a device for
these units are modified in accordance with MWO
shunt-feeding stages V5 and V6. Volt-
SIG 11-2258-2). Refer to a(2) above and figure
age across the synchronous motor wind-
38. Tubes V5 and V6 are connected in parallel in
ing and across T6 is approximately equal
all models of the equipment and serve as single-
and may rise as high as 1,000 volts.
ended, zero-bias, Class B, power amplifier tubes
Capacitor C30, by limiting transients,
whose output drives the synchronous motor.
prevents high peak voltages that might
(1) Facsimile Transceivers TT-1/TXC-1 and
break down insulation if the motor
winding.
In Facsimile Transceiver
grids (pin 5) of V5 and V6 is applied from
TT-1A/TXC-1, MOTOR FUSE F1 has
V4 through transformer T1. The plate
been added in the plate circuit of tubes
circuit of V5 and V6 consists of two
V5 and V6. Capacitor C31 prevents
parts; a dc circuit to supply plate current
arcing at the START switch contacts.
to the tubes and a series-resonant circuit
Normally, the +450-volt circuit to the
at 1,800 cycles to power the motor. The
plates of V5 and V6 is completed through
dc circuit consists of the synchronous
the START switch contacts, but when
motor winding and choke T6. The
the START switch is operated to ener-
series-resonant circuit consists of two
gize the separate start windings, the
series capacitors, C28 and C29, and the
synchronous winding of the motor is dis-
synchronous motor winding, which is
shunted by capacitor C30 to limit tran-
connected and the plates of V5 and V6
sients. The synchronous motor winding
are not energized.
81
