Model 618B Sect.111 Page 3
the pulse multivibrator, a positive voltage pulse
appears at the plate of V104A.The pulse width is
narrow, essentially two microseconds.
RUNNiNG
The positive output pulse is applied to the sync
amplifier tube V105A shown in Figure 3-7 and to
PULSE SERIES DIODE sync out cathode follower V105B shown in Fig. 3-6.
CLIPPER
NEGATIVE DELAYED
B. SYNC OUT CATHODE FOLLOWER
LIMITER PULSE
SHAPER
This stage provides the undelayed sync output
signal for synchronizing external equipment. It is
a standard cathode follower comprised of VlOSB,
one-half of a type 5814 dual triode tube. The out-
put is taken across R129, the cathode resistor, and
is capacitively coupled to the SYNC OUT connector
5102 by C118. Resistor R130 is returned from the
Figure 3-5. Block Diagram of Modulator
center conductor of the connector to ground so that
Circuits
the line is terminated in reference to ground in-
stead of the 300 vdc potential existing at the base
of the cathode resistor.
A. PULSE SHAPER
The output of the cathode follower is a positive
The pulse shaper (Figure 3-6) is a one-shot pulse greater than 25 volts when applied to a load
multivibrator with a two-microsecond time con- having a resistance of from 1000 to 100,000 ohms
stant. It consists of V104A and V104B, two halves and a shunt capacitance of 500 ppf. At no load,
of type 5814 dual triode. In the steady-state con- the pulse will have an amplitude of up to 55 volts.
dition, V104A is drawing current as its grid is
returned to the cathode by resistor R121. V104B
is cut off as its grid is returned to -300 vdc, thus
C. PULSE AMPLIFIER
placing a bias on the grid developed by the flow of
current through V104A and cathode resistor R120. The pulse amplifier is comprised of VlOSA,
one-half of a type 5814 tube as shown in Figure
3-7, and its associated components. It amplifies
When this multivibrator is triggered by the nega- and inverts the two-microsecond pulse provided
tive going leading edge of the wave generated by by the pulse shaper and provides negative pulse at
ti in its plate circuit. It also provides a positive-
going pulse in its cathode circuit from C115 that
is employed to trigger the saw-tooth generator
when internal frequency modulation is employed.
C115 acts as a cathode bypass capacitor when in-
ternal pulse modulation is employed.
D. SERIES DIODE BASE LIMITER
The negative pulse from the plate of the pulse
amplifier is applied to the cathode of the diode
limiter V106A shown in Figure 3-7. This limiter
is so connected that only the negative components
with an amplitude greater than the bias on the diode
-3OOVDC
will pass on to the cathode of the delay multi-
PULSE SHAPE MULTIVIBRATOR SYNC OUT CATHODE FOLLOWER
10 vibrator. This prevents triggering the multivi-
brator by any positive or low amplitude negative
Figure 3-6. Pulse Shaping Multivibrator and transients that may appear on the output of V105A
Sync Out Cathode Follower in addition to the desired trigger pulse. |
ACEC
