Tektronix 502 series, Instruction Manual

Page: 35 / 114

slower sweep-rates, however, the stray capaci­
tance 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
ASTIGMATISM control. A single control R841
adjusts the geometry of the display, and a single
INTENSITY control controls the brilliancy of both
beams. An INT. BAL control R860 balances one
grid voltage against the other so that the IN­
TENSITY control will have an equal effect on
both beams.
CALIBRATOR
The Calibrator is a square-wave generator
whose approximately 1-Kc output is available at
a front-panel connector labeled CAL. OUT. It
consists of a Multivibrator V873A-V875 con­
nected so as to switch the cathode-follower
V873B between two operating states— cutoff
and conduction.
During the negative portion of the multivibra­
tor waveform the grid of V873B is driven well
below cutoff and the cathode rests at ground
potential. During the positive portion of the
waveform the grid rises to slightly less than
+ 100 volts. By means of the CAL. ADJ. R879
the grid voltage can be adjusted so that the
cathode voltage is exactly +100 volts when the
SQUARE-WAVE CALIBRATOR knob is turned to
the OFF position.
The Cal. Out C.F. has a precision voltage divi­
der for its cathode resistor. By means of the
SQUARE-WAVE CALIBRATOR switch six cali­
brated peak-to-peak voltages, from 1 millivolt
to 100 volts, are available.
® CIRCUIT DESCRIPTION — TYPE
5 0 2
4-n