dropping resistor R37 and through drop-
TT-1E/TXC-1 and TT-1F/TXC-1 (fig.
ping resistor R38 and the primary wind-
The motor amplifier
of Facsimile Transceivers TT-1D/TXC-
The screen is not bypassed to ground.
1, TT-1E/TXC-1, and TT-1F/TXC-1
and 1C model transceivers, except for the
amplifier driver circuit of Facsimile
following changes which allow for a 900-
Transceiver TT-1B/TXC-1 or TT-1C/
cps signal at half-speed operation:
TXC-1 is similar to that described in
(1) above for earlier models of the equip-
(a) Speed control switch (30RPM-
ment, except that the grid and cathode
60RPM), S4, in series with the 1,800-
circuits of tubes V4 have been redesigned.
cps fork output to V4, and a multi-
Potentiometer R93 has been added to the
grid circuit of V4 so that proper adjust-
added. In the 60RPM position, the
ment may be made of the input to V4
1,800-cps fork output is coupled di-
which, in turn, affects the drive of stages
rectly to the grid of V4 through
V5 and V6. Resistor R93, located on
MOTOR JACK J6. For half-speed
MOTOR CURRENT meter M2, is ad-
operation of the scanning drum
justed for proper motor current reading
(30RPM), the 1,800-cps fork signal
on this meter. Cathode current of V4 in
Facsimile Transceiver TT-1B/TXC-1 or
(V26, 7N7), the output of which is
TT-1C/TXC-1 flows through the series
applied to the grid of V4 through
combination of R66, control R97, and
MOTOR JACK J6.
R67 of V13 in parallel with the phasing
(b) Capacitor C62 has been added to the
plate circuit of V4 as an ac bypass.
details of V13 cathode circuit.
(c) Capacitor C61 has been added between
Note. The value of R66 is changed from 1,500
R34 and R93 to ground to improve the
ohms to 750 ohms in the motor amplifier driver
900-cps waveshape. To stop the motor
stage of Facsimile Transceivers TT-1B/TXC-1
during standby periods, the grid of V4
and TT-1C/TXC-1 to compensate for the ad-
(pin 6) is short-circuited to ground
dition of R97 to the cathode circuit of V13.
Figure 41. Motor amplifier driver, Facsimile Transceivers TT-1B/TXC-1 and TT-1C/TXC-1.