Tektronix TU-7, Инструкция по эксплуатации

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Circuit Description— Type TU-7
Fig. 3-6. Timing o f chopped b la n k in g pulses from Type TU -7 lo oscilloscope crt cath ode w ith TEST FUNCTION switch a t CHOPPED.
A second output is produced in the plate circuits of the
multivibrator and coupled out through C100 and C l02. Each
time the multivibrator switches states, the voltage in the
plate circuit of one tube drops fast as the tube turns on,
stays at the lower voltage level until the other tube turns on,
then rises slowly to its maximum value as the capacitance
charges through a relatively high impedance path. The wave­
forms produced in both plate circuits of the switching mul­
tivibrator are coupled through Cl 00 and C102 to the cath­
ode circuit of V102B where they are combined and applied
through Cl 05 and pin 16 of the interconnecting plug to the
oscilloscope blanking circuit. The frequency of the composite
output chopped blanking signal is twice the repetition rate
of the switching multivibrator. See Fig. 3-6. This output
signal is inverted and amplified in the oscilloscope and
applied to the crt cathode to blank the crt beam during the
switching portions of the signal sent to the vertical amplifier
through pin 1 of the interconnecting plug.
PULSE GENERATOR CIRCUIT
General Operation
The Pulse Generator circuit consists of rate generator
multivibrator Q45/Q55, constant-voltage transistor Q33,
current-switching transistors, Q64/Q74, and disconnect diodes
D64, D65, D74 and D75. Fig. 3-7 is a simplified schematic
of the circuit. When the TEST FUNCTION switch is set to the
+ PULSE or — PULSE position, the rate generator operates
as an astable circuit. One complete multivibrator cycle turns
the current-switching transistors on and off. As these tran­
sistors are turned on, they shunt across the disconnect diodes
which then cut o ff very fast, producing the fast-rise step-
function output (see Fig. 3-8). As the current-switching tran­
sistors are turned off again, the disconnect diodes conduct
again and the output pulse ends (see Fig. 3-9).
Detailed Operation
For the following discussion, assume that the TEST FUNC­
TION switch is set to the + PULSE position and the AM­
PLITUDE control is turned fully clockwise to the maximum
amplitude position. The TEST FUNCTION switch connects the
+ 100-volt supply to the collector circuit of Q33, and ap­
plies about + 7 5 volts to the base of the transistor through
D30 and R30. The transistor is thus turned on with emitter
current provided through D35 and R39 from ground. When
the circuit is correctly adjusted, the voltage at the emitter
of Q33 is approximately + 7 5 volts, providing all positive
supply voltages for the Pulse Generator circuit. The + 6 0
volts existing at the anode of D35 provides the supply volt­
age for the base circuits of the rate generator multivibrator
and for one end of the amplitude control network. DRIVE
BAL R40 is adjusted so the push-pull output voltages are
equal.
As soon as supply voltages are applied to the circuit, the
rate generator begins its astable multivibrator operation.
During the multivibrator cycle, when Q45 is conducting and
Q55 is cut off, the positive voltage at the collector of Q55
reverse biases the base-emitter junction of Q74, holding
3-7