Tektronix 570, Руководство пользователя

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R 9 1 and R92. As the waveform goes positive , a
point will be reached where the voltage from the
Step-Control Cathode Follower, VSSB , is suffi­
cient to switch the Multivibrator. When this
h appens C8S is dischraged and the Step Generator
s t arts over again. R8S labeled MIN NO CUR YES
is normally adjusted so the Step Generator will
have four steps when the STEPS/F AMIL Y Control
is counterclockwi se.
S T E P A M P L I F I E R DIAGRAM
I n p ut Cathode Follower
The incoming step waveform passes through
a level-s etting voltage divider , R 1 l 2 , R l l S and
R 1 20 , and into cathode follower V l l S B . V l l S A
s erves a s a voltage regulator to regulate the
voltage from the unreg 400 volt supplies
used for this stage.
Input A m p l ifiers
V l l O and V 1 3 S are common-c athode. phase­
splitter amplifiers. The VOLTS/STEP ZERO
ADJ Control , RlOS . sets the grid level of
V 1 10 to balance the amplifie r so the zero
bias trace does not shift as the VOLTS/STEP
Control is rotated. C l 2S and C 1 26 reduce the
b andwidth of this stage to maintain stability
with the large amount of feedback used.
Output Amplifiers
The Output Amplifi ers , VlS0A and VlS0B ,
amplify the waveform and reconvert it to
single-ended output.
The network including
the neon diode B 17 0 reduces the dc level of
the signal at the grid of V180 without atten­
u ation of the signal.
Output Cathode Follower
The Output Cathode Follower. V 1 80 , provides
the necessary low impedance to drive the grid
of the device being tested. The Z E RO BIAS
switch . SW180 , grounds the GRID A or G RID B
connector on the test panel to provide a zero­
bias reference curve. The TEST POSITION
s witch connects the output of the Step Amplifier
to either the GRID A or GRID B connector on
the test panel.
VOL TS/STEP Control
The VOLTS/STEP Control varies the amount
of feedback and thus . the gain of the Step
Amplifier is seven fixed steps. This determines
the grid-voltage change between the curves in
the display.
Grid-Current Measurement
In order to measure grid current in the
device being tested , the grid current must
flow through the current measuring circuits.
Any current used to operate the Step Amplifier
must be kept separate. To do this the Output
C athode Follower is supplied with plate and
c athode voltage from an ungrounded or Floating
Power Supply. The only path though which
c urrent will flow from ground into this power
supply is from grid to cathode in the device
being tested and through the current-measuring
resistors.
Since the Input Cathode Follower is connected
to the Output Cathode Follower by the feedback
resistors , it is als(') connected to the F loatiI!g
Power Supply.
H O R I Z O NTAL AMPLI F I E R
V O L TS/ D I V . Switch
The Input Cathode Follow er, V 2 1 S , presents
a high impedance to the circuits being measured
and a low impedance to the
part of the
VOL TS/DIV switch in its cathode circuit. Part
of the attenuation of the VOL TS/DIV switch
is placed in the grid circuit so that the input
voltage will not exceed the capabilities of the
Input C athode Follower.
This attenuator in
the grid circuit is switched so that the current
it draws will not be measured by the current
measuring circuits in any position of the PLA TE­
S C REEN-GRID switch.
The VOL TS/DIV B AL Control R2 1 4 , adjusts
the dc level on the grid of cathode follower
V 210. This control is set so there is no shift
of the zero-voltage line as the VOL TS/DIV
Control is rotated.
The VOL TS/DIV CAL
Control compensates for the loading effect
of the attenuator on the cathode follower.
Amplifiers
The first amplifiers . V240 and V24 1 . are
c ommon-cathode, phase-splitter amplifiers
The bandwidth of this stage is limited by C242
for stability with feedback. The second stage,
V24SA and V24SB, provides additional gain to
drive the crt deflection plates . The HORIZ
AA C i rcuit Description - Type 570
3 - 3