Tektronix 535A, Инструкция по эксплуатации

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Circuit Description — Type 535A
Alternate-Trace Operation
Alternate-trace operation is available with Tektronix con­
vertible oscilloscopes by employing the 53C, 53/54C or
Type CA plug-in preamplifiers. Additional circuitry in the
Time-Base Generator circuit provides a pulse to 'flip" a
bistable multivibrator in the plug-in. This multivibrator pro­
vides a change in dc level at the inputs of the amplifiers in
the plug-in. This change in dc level is used as a positioning
voltage which separates the two traces a distance selected
by the operator.
The Time-Base Generator circuitry necessary for alternate­
trace operation utilizes an amplifier which amplifies the sig­
nal present at the grid of V154A. The signal at the plate
of the amplifier, V154A, is connected to pin 16 of the inter­
connecting socket, while the signal at the cathode is con­
nected to pin 8 of the interconnecting socket. Fig. 4-3 shows
the Time-Base Generator circuitry involved. Fig. 4-6 shows
the plug-in circuitry which affects the positioning.
Negative-going pulses, generated at the end of each
time-base by the Sweep-Gating Multivibrator in the Time-
Base Generator, are amplified by the amplifier, V154A. The
pulses are coupled through the interconnecting socket to the
Trigger Coupling Diode in the plug-in. Each trigger causes
the multivibrator to “flip" from one stable state to another
at a rate determined by the repetition rate of the Time-Base
Generator.
The square-waves present at the cathodes of the multi­
vibrator tubes are used to drive the amplifiers, V3384A and
V3384B. The signals from these amplifiers are used to drive
V3393B and V3393A; cathode followers which isolate the
multivibrator circuitry from the signal amplifiers. The output
of the cathode followers raises or lowers the plate voltage
of the Input Amplifiers as the multivibrator passes from one
stable state to the other.
In later Tektronix instruments an additional stage has been
added in the Time-Base Generator to provide blanking when
the plug-in is operated in the CHOPPED MODE. This is
shown as V154B in Fig. 4-3. In the CHOPPED MODE of
operation the multivibrator in the plug-in free runs at a
rate determined by circuit constants. Transients generated
during free-running operation are blanked from appearing
on the crt screen by the action of V154B.
Horizontal Amplifier
The Horizontal Amplifier converts the single-ended saw­
tooth output of the Time-Base Generator into push-pull
signal suitable for driving the horizontal plates of the crt.
The gain of the amplifier may be varied by a factor of five
by means of the 5X magnifier switch. In addition, controls
are provided for horizontal positioning and adjustment of
the horizontal linearity.
The sawtooth waveform from the Time-Base Generator is
coupled to the Input Cathode Follower through the R330,
C330 network. This network attenuates the input signal
and provides a means of compensating the input circuitry
for optimum frequency response. During calibration C330
is adjusted for best response to a square wave.
The HORIZONTAL POSITION and VERNIER controls ad­
just the dc level at the grid of V343A. This change in dc
level changes the dc level on the signal path through the
amplifier, thus changing the dc voltage applied to the crt
horizontal deflection plates and affecting horizontal position­
ing.
Coupling between the Input CF and the Driver CF is made
by the 5X MAGNIFIER switch. When this switch is in the
OFF position the signal from the Input CF must pass through
the network formed by C348 in parallel with the series
combination R348, and R349. R348, a variable resistor,
allows the operator to adjust the length of the time base
by varying the attenuation applied to the signal. C348, a
variable capacitor, is adjusted to provide optimum linear­
ity of the time base on the fastest time bases.
This network attenuates the signal by a factor of five. To
provide magnification of the time base, the network is re­
moved when the 5X MAGNIFIER switch is turned to the ON
position.
The gain of the Horizontal Amplifier is controlled by a
negative feedback circuit. The signal appearing at the left­
hand deflection plate is fed back to the input of the Driver
CF. R358 is an adjustable resistor which allows the operator
to vary the dc voltage applied to feedback loop.
By changing the de voltage at this point the operator can
adjust the position of the unmagnified sweep so that it will
correspond with the position of the magnified sweep.
The output waveform from the Horizontal Amplifier is
taken from V364A and V384A. The cathodes of these tubes
are connected through a network which includes the Mag.
Gain control. This control enables the operator to adjust the
gain of the Horizontal Amplifier so that the ratio between
the magnified and unmagnified sweeps is correct. C375,
in parallel with the Mag. Gain control, has considerable
effect on the linearity at the beginning of the time base,
and is adjusted while displaying a signal with a high repeti­
tion rate.
Part of the signal appearing at the plates of the output
amplifiers is used to drive the Output CFs. Note that the
cathode of V364B is connected to the plate of V398, a pent­
ode.
The function of the Output CFs is to drive the capaci­
tance of the horizontal deflection plates and the associated
wiring. To assure a sufficient flow of current at fast time
bases, the pentode, V398 is used to supply current to the
Output CF which drives the negative-going, or left-hand
deflection plate. A pentode is chosen as a current booster,
since its plate characteristic provides a flat-topped pulse of
current. The pulse to drive the grid of the pentode is de­
rived from the waveform at the right-hand deflection plate.
This waveform is differentiated by the C390, R390 network
before
being applied to the grid. Its amplitude is thus pro­
portional to the time base. For the fastest time bases,
the tube current is several times normal, but at the reduced
duty cycle of the time base, well within the dissipation
rating of the tubes.
Bootstrap capacitors C364 and C384 are used to help
supply the necessary charging current for fast time bases.
During calibration these two capacitors are adjusted on the
fastest time base for optimum linearity.
4-11