lamp amplifier circuit, and the photoed bridge
modulator circuit.
Dual triode tube V2 (7N7) serves as the fork input
(1) Motor amplifier buffer. Triode section 5,
amplifier and fork driver.
6, and 7 of V3 is the motor amplifier
(1) Fork input amplifier. Pins 2, 3, and 4
comprise the fork input amplifier which
buffer. Its grid receives 1,800-cycle
is fed 1,800-cycle energy generated in the
energy from the plate circuit of V1
through coupling capacitor C303 and
pick-up coil by the vibrating fork. Re-
sistor R302 is the unbypassed cathode re-
limiting resistor R314. The grid resistor
sistor. Plate voltage is applied to pin 3
is a combination of R315 and R318, with
from the regulated +250-volt supply
the grid of the second section of V3 fed
from a tap between these resistors.
through plate load resistor R301. The
Capacitor C310 is an hf bypass for the
output developed across the resistor is
grid. Resistor R316 is the unbypassed
coupled to the grid (pin 6) of the second
fork amplifier V1 (7L7) through coupling
cathode resistor. The signal at the plate
developed across load resistor R308 is
capacitor C304.
(2) Fork driver. Pins 5, 6, and 7 comprise the
coupled through C302 to motor ampli-
fork driver. Input to the grid (pin 5) is
fier stage V4 via the MOTOR JACK
received from the plate of V1 through
and control switch S4, and also to the
exciter lamp amplifier circuit of Rectifier
coupling capacitor C303 and series re-
Power Unit PP-86(*)/TXC-1.
sistor R305. Limiting resistor R305 and
grid resistor R306 serve, as a voltage
Note. In Facsimile Transceivers TT-1D/
TXC-1, TT-1E/TXC-1, and TT-1F/TXC-
divider for the input to this section of
1, the motor amplifier buffer output is cou-
V2, Regulated +250 volts is supplied
pled to motor amplifier stage V4 through
through plate load resistor R307. Out-
the motor speed control switch S4 permitting
put from the plate is coupled through
selection of either the 900-cycle output of the
C301 to the drive coil which keeps the
multivibrator (half-speed operation), or the
fork oscillating. The cathode circuit
1,800-cycle fork unit output. The selected
output is applied to the grid of V4 through
consists of two unbypassed resistors:
MOTOR JACK J6. In Facsimile Tranceiver
fixed resistor R303 and variable resistor
TT-1B/TXC-1, a connection to IIIR of selector
R304. Adjust R304 to compensate for
switch S1C short-circuits the 1,800-cycle motor
minor changes in the frequency of the
circuit and exciter lamp supply when the selector
switch and the STANDBY-MON-TALK switch
fork.
are both at STANDBY. In Facsimile Trans-
ceiver TT-1C/TXC-1, a connection to the front
amplifier V1 (7L7) is an amplifying link in the
of IIIR of selector switch S1C opens the B+
oscillator circuit composed of the fork, the input
circuit in the motor lead, and the connection to
amplifier, the second fork amplifier, and the fork
the back of contact IIIR of the selector switch
short-circuits the 1,800-cycle exciter lamp circuit
driver. The grid (pin 6) is fed from the plate
supply when the selector and STANDBY-MON-
(pin 3) of V2 through coupling capacitor C304.
TALK switches are at STANDBY. (Refer to
The grid voltage is developed across resistor R313.
Cathode resistor R310 is bypassed by C306.
T X C - 1 , TT-1E/TXC, and TT-1F/TXC-1 the
Screen voltage is supplied through dropping re-
motor is stopped by short-circuiting to ground
the grid of motor amplifier tube V4 through the
sistor R311 and the screen is bypassed to cathode
contacts of the STANDBY-MON-TALK switch
by C305. The plate load resistor is R312 and the
and section 6 of the selector switch when both
1,800-cycle output from the plate (pin 2) is coupled
switches are operated at the STANDBY position.
to the fork driver through C303 and limiting re-
The exciter lamp supply is short-circuited to
sistor R305, Part of the output of V1 is applied
ground through section 2 with the selector switch
at STANDBY.
to the dual buffer output stage V3 through limiting
resistor R314.
(2) Modulator buffer. Triode section 2, 3, and
4 of V3 is the modulator buffer. Its grid
output stage V3 is a 7N7 dual triode tube. It con-
(pin 4) receives the 1,800-cycle energy
developed across R318, as explained in
sists of two buffer amplifiers, fed by second fork
(1) above. Resistor R317 is the unby-
amplifier V1. This tube supplies an 1,800-cycle
The plate
passed cathode resistor.
signal to motor amplifier stage V4, the exciter
