Tektronix 502A, Instruction Manual

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Circuit Description—Type 502A
network composed of R864, C868, C869 and R868 for one
grid circuit, and R864, C866, C867 and R866 for the other,
is employed. By this arrangement, the fast leading edge of
the unblanking pulse is coupled directly to the grids of the
crt via (C866, C867) and (C868, C869). For short-duration
unblanking
pulses (at the faster sweep rates) the power
supply itself is not appreciably moved. For longer unblank­
ing pulses, at the slower sweep-rates, however, the stray
capacitance of the circuit is charged through R864. This
holds the grids at the unblanked potential for the duration
of the unblanking pulse.
Each gun of the crt has its own FOCUS and ASTIG­
MATISM Controls. A single control R841 adjusts the geo­
metry of the display, and a single INTENSITY Control
controls the brilliance of both beams. An INTENSITY
BALANCE Control R860 balances one grid voltage against
the other so that the INTENSITY Control will have an equal
effect on both beams.
AMPLITUDE CALIBRATOR
The AMPLITUDE CALIBRATOR is a square-wave gen­
erator whose approximately 1-Kc output is available at a
front-panel
connector labeled CAL OUT. It consists of a
Multivibrator V873A-V875 connected so as to switch the
cathode-follower V873B between two operating states,
cutoff and conduction.
During the negative portion of the multivibrator wave­
form the grid of V873B is driven well below cutoff and the
cathode rests at ground potential. During the positive por­
tion of the waveform the grid rises to slightly less than +50
volts. By means of the CAL AMPL (R879) Control, the
grid voltage can be adjusted so that the cathode voltage
is e50 volts when the AMPLITUDE CALIBRATOR
knob is turned to the OFF position.
The Cal Out CF has a precision voltage divider for its
cathode resistor. By means of the AMPLITUDE CALIBRATOR
switch six calibrated peak-to-peak voltages, from .5 milli­
volt to 50 volts, are available.
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