Tektronix 507, Instruction Manual

Page: 18 / 60

CATHODE-RAY TUBE CIRCUIT
The NE2 neon glow lamps across the INTEN­
SITY control potentiometer and MAX. INTENSITY
variable resistor maintain the INTENSITY poten­
tiometer terminal voltage constant regardless of
cathode-ray
tube cathode current, thereby
stabilizing the intensity adjustment.
The purpose of the MAX. INTENSITY control
is to adjust the minimum grid bias setting avail­
able by the INTENSITY control to a safe value
thus preventing damage to the cathode-ray tube
screen in case the INTENSITY control is ad-
HIGH-VOLTAGE
All accelerating potentials for the cathode-
ray tube are provided by a high-voltage supply
employing an audio oscillator operating at a
frequency of approximately 1500 cycles. Four
high-voltage rectifier tubes in a voltage-quad-
van ced too far.
The FOCUS control potentiometer varies the
voltage at the focusing ring to focus the trace;
the ASTIGMATISM control potentiometer varies
the voltage at the astigmatism anode to focus
the spot in both dimensions simultaneously.
The GEOM. ADJ. potentiometer varies the
field as the beam emerges from the deflection
system to control the linearity at the extremes
of deflection.
POWER SUPPLY
k
rupling circuit provide +20,000 volts; a single
half-wave rectifier tube provides —4000 volts.
The high-voltage rectifiers, capacitors, resistors
and transformers are all oil-immersed.
HIGH-VOLTAGE OSCILLATOR A N D REGULATOR CIRCUIT
The screen voltage of the high-voltage oscil­
lator V820 is regulated to maintain a con­
stant —4000 volts of rectified output so that
the deflection sensitivity of the cathode-ray
tube will not be affected by line-voltage
or load changes. A sample of the —4000-volt
output, obtained from a tap on the divider con­
sisting of R212 and R213, is compared to the
regulated —250-volt supply through V814A. Any
“ error” voltage that may exist is amplified by
V814A and V814B and is applied to the screen
of the oscillator tube V820. This will change the
output of the oscillator in a direction to compen­
sate for the error. The —4KV ADJ. R814 controls
the bias on V814A and is adjusted so that the
output voltage is exactly —4000 volts. This same
circuit indirectly regulates the +20,000-volt sup­
ply since the oscillator furnishes energy for both
supplies.
The time-constant network associated with the
V804 circuit delays the application of screen
voltage to the oscillator tube slightly when the
power is first turned on. This permits the oscil­
lator circuit for the heaters (V830) to bring the
heaters up to emission before the application of
plate voltage in the rectifier tubes.
TIME-MARK GENERATOR
An electron-coupled Colpitts oscillator V250B
is gated off and on by a free-running multi­
vibrator circuit V225A and V225B through the
cathode-follower V250A. The gated time markers
are then amplified in V264 and are coupled to
the cathode-ray tube vertical deflection circuit
when the SIGNAL MODE switch is in the MARK­
ER position.
The time markers are also coupled through
C267 to the grid circuit of the cathode-follower
V243A, where they are superimposed on the
multivibrator waveform and fed to the trigger
circuitry so that the sweep can be triggered by
the markers when the TRIGGER SELECTOR switch
is in the MARKER position. The diode V242
clamps the grid of V243A to prevent the nega­
tive pulses of the differentiated multivibrator
waveform from producing a trigger.
i t
2-4
CIRCUIT DESCRIPTION — TYPE 5 0 7
®