Tektronix 511A-AD User manual

CATHODE-RAY OSCILLOSCOPE
TYPE 511A-AD
SERIAL NUMBER _________________________
INSTRUCTION
MANUAL
MANUFACTURERS OF CATHODE-RAY AND VIDEO TEST INSTRUMENTS
Sunset Highwa and Barnes Road • P.O.Box 831 • Portland 7, Oregon, U. S. A.
Phone: CYpress 2-2611 • Cables: Tektronix

SECTION I
GENERAL DESCRIPTION
The Tektronix Type 511-A Cathode Ray Oscillo
scope is a wide range, portable instrument, making
possible the observation of a wide variety of electrical
waveshapes. It is primarily intended for laboratory and
shop use, in the development and testing of all types of
electronic equipment.
The Type 51 1-AD Oscilloscope is identical to the Type
511-A except that it includes a factory installed Type
l-AD-25 Delay Network,
CHARACTERISTICS
Signals observable
1. Sine waves from 10 cycles to 10 m c .
2. Pulses of .1 microsecond to 1/50 sec.
Sweep Circuit
Hard tube type, either triggered or recurrent as de
sired.
Sweep Speeds
Continuously variable from .01 sec. per cm to .1 micro
second per cm.
Trigger Requirements
.5 to 50 V (Peak) sine wave or pulse of either polarity.
Pulse as short as .05 microsecond will trigger satis
factorily. A key connected between TRIGGER INPUT
and GND. is suitable for triggering single sweeps.
Sweep Lag
CRT is unblanked and sweep is operating linearly in
less than .1 microsecond after receipt of an infinitely
sharp trigger pulse.
Sweep Magnification
Any desired 20% of the sweep can be spread over the
entire trace except for sweep speeds faster than .5
microsecond per cm.
External Sweep Input
DC coupled via 100 K potentiometer and sweep am
plifier.
Maximum deflection sensitivity 1.5 V per cm DC or
peak to peak AC. Band width, DC to 800 kc (3 db
down at 800 kc).
Vertical Deflection Circuit
Switch permits signal input connector on panel to be
connected to deflection plates directly, via capacitor
(RC = .l sec), via 1 amplifier stage, or via 2 amplifier
stages.
Input Attenuator
Frequency compensated RC type with attenuation
ratios of 2, 4, and 8.
Vertical Deflection Sensitivity
Without amplifier 27 V per cm maximum, 200 V per
cm minimum, DC or peak to peak AC.
1 Stage, 2.7 V per cm maximum, 40 V per cm mini
mum.
2 Stages, .27 V per cm maximum, 4 V per cm mini
mum.
(Sensitivity is reduced by a factor of 10 when probe
is used.)
In no case should the combined AC and DC input
voltages exceed 600 V peak
Input Impedance
1 meg shunted by 40 mmfd (±5%) for any setting of
the input selector and input attenuator.
With probe, 10 megohms shunted by 14 mmfd.
Vertical Amplifier Bandwidth
1 stage, down 3 db (Max) (from 1 m c response) at 5
cps and 10 m c .
2 stages, down 3 db (Max) (from 1 m c response) at 5
cps and 8 m c .
Vertical Amplifier Transient Response
Rise time, 1 stage .04 microsecond (10% to 90%)
2 stages .05 microsecond (10% to 90%)
Calibrating Voltage
Clipped sine wave of power line frequency. Six
ranges 0-.3, 0-1, 0-3, 0-10, 0-30, 0-100 volts peak to
peak. Accuracy for line voltages from 105 to 125 v. is
zt3% of full scale. A position on the SIGNAL CALI
BRATE switch allows the use of an external calibrat
ing source when desired.
Waveforms available externally.
Sweep sawtooth, 20 volts peak.
Positive and negative gate, 40 V. peak, same dura
tion as sweep.
Connection to CRT Cathode
via .1 mfd capacitor. RC = . 0 12 sec.
Accelerating voltage on cathode ray tube, 3 KV.
Power Requirements. 105-125 volts, or 210-250 volts,
50-60 cycles, 230 watts. (See Section IV.)
Weight. 50 pounds.
Dimensions. 15½" high, 12½" wide, 21 ½" deep.
Finish. Panel, photo etched aluminum with black letters.
Cabinet, gray wrinkle.
FUNCTIONS OF CONTROLS AND
BINDING POSTS
A brief explanation of the function of each control and
binding post is given on the next page. For a more de
tailed explanation consult Section III, Circuit Description.
SECTION 1, PAGE 1
TYPE 511-A, 51 1-AD

PANEL MARKINGS
EXPLANATION
INTENSITY
INPUT CHAN.
SEL.
Gang switch permitting the input
signal to be connected to the vertical
deflection plates either directly, via a
.1 mfd capacitor, 1 stage amplifier, or
2 stage amplifier.
Potentiometer controlling the average
grid voltage of the CRT and thereby
the brightness of the image.
POWER
On-off switch in the AC line voltage
supply to the oscilloscope.
INPUT
ATTENUATOR
Four position RC compensated attenu
ator located between the SIGNAL
CALIBRATE switch and INPUT CHAN.
SEL. for reducing the voltage of signals
which would otherwise produce exces
sive deflection or overload the ampli
fiers.
FOCUS Potentiometer controlling the voltage
applied to the focus anode of the CRT
and thereby the sharpness of the
image.
VERT. AMPL.
ATTEN.
500 ohm potentiometer in cathode of
cathode follower permits adjusting
gain of signal amplifier.
HOR. POSITION Potentiometer controlling the bias ap
plied to grid of one sweep amplifier
tube and thereby the position of the
image.
SWEEP Binding post connected to sweep gen-
OUTPUT erator via cathode follower.
SIGNAL —
CALIBRATE
Switch which connects arm of INPUT
ATTENUATOR to EXT. CAL. binding
post, SIGNAL INPUT binding post, or
line frequency calibrating voltages.
SWEEP
MAGNIFIER
POSITION
SIGNAL INPUT Coaxial connector permits connection
of the low capacity probe or binding
post adapter.
Potentiometer controlling voltage ap
plied to grid of sweep magnifier (V 1 1)
and thereby determining portion of
sweep to be magnified. When turned
to OUT sweep magnifier is discon
nected from the circuit.
DELAY
(511 -AD only)
Two position switch which permits the
Type 1AD25 Delay Network to be
switched in or out of the video ampli
fier.
SWEEP SPEED
MULT.
Decade control plus vernier control
setting sweep speed and duration
within range indicated by SWEEP
RANGE.
VERT.
POSITION
Twin potentiometers controlling aver
age potentials of vertical deflection
plates and therefore the image posi
tion.
EXT. SWEEP
ATTEN.
Potentiometer controlling the fraction
of the voltage applied to EXT. SWEEP
INPUT binding post which will reach
the grid of the sweep amplifiers when
the SWEEP RANGE switch is set in the
EXT. position.
CAL. VOLTAGE Potentiometer for adjusting the clipped
sine wave calibrating voltage of line
frequency on ranges determined by
the setting of the SIGNAL CALIBRATE
switch.
CRT CATHODE Binding post permitting connection of
external modulating signals to the
cathode of the cathode ray tube via a
.1 mfd capacitor. RC=. 0 12 sec.
GND. Connection to frame of oscilloscope.
ASTIGMATISM Potentiometer varying potential on
Anode No. 2 with respect to the de
flection plates. Correct adjustment of
this control makes possible a sharp
focus of the image in both directions
simultaneously.
SCALE ILLUM. Variable resistor controlling brightness
of the lamp which illuminates the plas
tic graticule over the face of the cath
ode ray tube.
EXT. SWEEP
INPUT
CAL. INPUT
CAL. OUTPUT
+ GATE
Binding post connecting to sweep am
plifier via EXT. SWEEP ATTEN. when
SWEEP RANGE switch is in EXT. posi
tion. (100 K input impedance).
Binding post connecting to EXT. CAL.
position of SIGNAL CALIBRATE switch
permitting an external calibrating sig
nal source to be permanently con
nected to the oscilloscope.
May be used as auxiliary signal input
Binding post connected to arm of
CAL. VOLTAGE potentiometer permits
use of internal calibrating voltage as
an external test signal of known am
plitude.
Binding post for connection to the cath
ode of the gate phase splitter (V8). This
furnishes a 40 V peak positive pulse of
the same duration as the sweep.
TYPE 511-A, 511-AD
SECTION 1, PAGE 2

- GATE
SWEEP
RANGE
Binding post for connection via .1 ca
pacitor to the plate of (V8). This fur
nishes a 40 V negative pulse of the
same duration as the sweep.
Gang switch selecting appropriate
coupling capacitors determining mul
tivibrator length and sweep speed.
When set to EXT. the sweep amplifier
is connected to EXT. SWEEP INPUT
post in place of the oscilloscope's lin
ear sweep.
TRIGGER SEL.
TRIGGER
AMPL.
TRIGGER
INPUT
SWEEP
STABILITY
Variable resistor controlling bias on
grid of V4 in the multivibrator circuit.
This bias determines whether the
sweep will operate recurrently or must
be triggered.
DEFLECTION
POLARITY
Switch determining source and polari
ty of trigger voltage.
Potentiometer controlling the bias ap
plied to the trigger amplifier tube (V2)
and thereby determining the ampli
tude of trigger signals applied to the
multivibrator.
Binding post connecting external trig
ger sources to + EXT. and — EXT. posi
tion of TRIGGER SEL. switch.
Three position lever switch mounted at
the rear, which permits the operating
bias of V 1 9 to be varied, thus providing
greater undistorted deflection when
observing pulses.
SECTION 1, PAGE 3
TYPE 511-A, 511-AD

SECTION II
OPERATING INSTRUCTIONS
The Type 511 -A may be operated in any normal in
door location, or in the open if protected from moisture.
If the instrument has been exposed to dampness, it
should be left in a warm room until thoroughly dry, be
fore being placed in operation.
To prevent excessive interior temperatures, it is im
portant to allow adequate ventilation for the oscillo
scope. Several inches clearance should be provided at
the sides, back and top of the case.
If the Type 511 -A is used continuously for the same
application, and only one setting of the controls is re
quired, it is advisable to periodically check the instru
ment at all control settings to be sure it is in normal
operating condition. For example, if only direct connec
tion to the vertical deflection plates of the CRT is used,
a defect in the vertical amplifier might not become evi
dent. Operation of the controls also helps to prevent
accumulation of dirt and tarnish on their contacts.
Although the components are well supported and the
adjustments very stable in setting to allow for portable
operation, the Type 511 -A should not be subjected to
excessive vibration or rough handling.
To place the Type 511 -A in operation for the first time
the following procedure is suggested.
1.
2.
Connect to a source of 50-60 cycle, 105-125 V power.
Set controls as indicated below.
INPUT CHAN. SEL...
INPUT ATTENUATOR
VERT. AMPL. ATTEN.
SIGNAL-CALIBRATE.
VERT. POSITION ........
CAL VOLTAGE ........
ASTIGMATISM ..........
INTENSITY ................
FOCUS ..........................
HOR. POSITION ........
SWEEP MAGNIFIER POSITION
SWEEP SPEED MULT.
SWEEP RANGE...
SWEEP STABILITY
TRIGGER AMPL...
TRIGGER SEL .......
.............. 1 STAGE
.......................... X 1
............ Clockwise
......................... 3 V
.... Index vertical
............................ 0
.. . Index vertical
Counterclockwise
.. . Index vertical
............. Clockwise
OUT
5.0
10,000
Counterclockwise
Counterclockwise
................... +INT.
Turn POWER switch to ON and wait about 30
3.
seconds.
4. Advance INTENSITY control until a spot is seen.
5. Adjust VERT. POSITION, HOR. POSITION, ASTIG
MATISM and FOCUS until a sharply focussed spot is
obtained at the left center of the screen.
CAUTION — DO NOT ALLOW THIS SPOT
TO BE EXCESSIVELY BRIGHT OR RE
MAIN FOR LONG IN ONE POSITION.
6. Advance the SWEEP STABILITY control until a
sweep appears, then turn it back just under this point.
7. Set the CAL. VOLTAGE control to 30. A vertical
line about 1.25 cm high should appear.
8. Advance the TRIGGER AMPL. control until a
stable image of a clipped sine wave appears.
The oscilloscope is now observing the 50-60 cycle
power line waveshape clipped by the calibrator cir
cuits.
To observe other waveshapes connect them to the SIG
NAL INPUT binding post, turn the SIGNAL CALIBRATE
switch to SIGNAL, select the appropriate sweep speed, etc.
SWEEP CIRCUIT ADJUSTMENTS
The sweep circuit of the Type 511 A is different from
the gas tube type usually employed in portable oscillo
scopes. It is much more flexible and capable of syn
chronizing with much higher frequencies than conven
tional sweep circuits. Fundamental frequencies of 10
m c and higher can be easily observed. By one simple
adjustment the sweep will run recurrently or triggered
as desired.
In a recurrent or sawtooth sweep as generated by a
gas tube or similar device the synchronization takes
place at the end of the sweep. The sync impulse causes
the beam to return to the left side of the tube where it
immediately starts another sweep. Thus the sweep time
must be a multiple of the signal period, or expressed
another way, the sweep frequency an integral fraction
of the signal frequency.
In a triggered sweep circuit each sweep is started in
dependently of the preceeding sweep by a trigger or
synchronizing impulse. When no trigger is being re
ceived, the beam remains at the left side of the trace.
When the trigger arrives, the beam goes linearity to the
right for a time in this case determined by the multi
vibrator pulse length. At the end of its sweep it returns
to the left side again to await another trigger. It is this
variable waiting period which makes the synchroniza
tion so easy since the sweep time is now independent
of the signal period. The triggered sweep makes it pos
sible to view pulses such as used in radar and tele
vision where the length of the pulse is very short com
pared to the space between pulses. This requires a fast
sweep with a long waiting period. Waiting periods of
2000 times the sweep length are frequently used.
Adjustment of Sweep Stability
The SWEEP STABILITY control varies the multivibra
tor bias and therefore detemines whether the sweep
will oscillate recurrently or wait for a trigger impulse.
Correct functioning for triggered operation is therefore
obtained when it is set just under the point where oscil
lation takes place. The procedure is to remove the
trigger source, turn the TRIGGER AMPL. control counter
clockwise, and advance the SWEEP STABILITY knob
until a sweep appears and then decrease it until it just
disappears.
SECTION 2, PAGE 1
TYPE 511-A, 511-AD

NOTE — When using the internal trigger im-
pulses to view fundamental frequencies
above about 2mc it will be necessary to
progressively advance the SWEEP STA
BILITY control somewhat above the normal
operating point to secure a stable pattern.
Function of Trigger Sei
This control selects the trigger impulse to be used
from three sources, the line frequency, (60 cycles), the
video amplifier ( + INT and — INT), or the TRIGGER IN
PUT binding post. Two positions are available for both
the INT. and EXT. sources. When using those marked
4- the sweep starts at the rising portion of the trigger
impulse. The — positions start the sweep on the falling
portion. When the INPUT CHAN. SEL. switch is in the
2 STAGES position the + INT and — INT positions are
reversed in polarity since the trigger impulses are shifted
180 º by the pre-amplifier stage. For satisfactory opera
tion in the EXT. positions a trigger of from 1 V to 50 V
peaks should be provided. Larger triggers should be
reduced by an external attenuator.
Adjustment of Trigger Ampl
The TRIGGER AMPL. control adjusts the bias in the
trigger amplifier and therefore the amplitude of the
impulse which reaches the multivibrator. After the
SWEEP STABILITY is set as described previously, and
the TRIGGER SEL. switch set to the correct position, ad
vance the TRIGGER AMPL. control until a stable image
is obtained. When the trigger source is a slowly chang
ing wave such as a sine wave or sawtooth, adjustment
of the TRIGGER AMPL. setting will change the phase
of the signal relative to the start of the sweep.
In general, it is desirable to use the minimum TRIG
GER AMPL. setting required to insure a stable image.
If poor synchronizing is experienced when the Type
511 -A is used to observe repetitive signals containing
erratic peak voltages, such as produced by vibrating
contacts, it may be possible to form a stabilized trigger
signal by the use of auxiliary limiting and differentiat
ing circuits. The TRIGGER SEL. switch should then be
set to the proper EXT. polarity, and connection made to
the TRIGGER INPUT.
Adjustment of Sweep Speed
The combination of SWEEP RANGE and SWEEP
SPEED MULT, controls allows the operator to vary the
sweep speed so that the marked portion of the grati
cule (10 cm) is covered by the trace in any time from
.1 sec. to 1 microsecond. The number of microseconds
required for the sweep to traverse the 10 cm. scale is
determined by multiplying the SWEEP RANGE reading
by the sum of the readings of the SWEEP SPEED MULT,
dials. This indicated reading is accurate within 5%
when calibrated at the factory. Provision has been
made to compensate for variations caused by different
tubes, etc., by a screwdriver adjustment inside the case.
Procedure for adjustment of this control is described in
Section IV.
Recurrent Sweep
In case it is desirable to have a sweep without using
any sort of trigger, merely advance the SWEEP STABILI
TY control until a stable sweep is obtained. This sweep
is the conventional sawtooth variety as used in most
oscilloscopes.
Single Sweep
The triggered sweep circuit used in the Type 511 in
herently provides for single sweep operation. The beam
is blanked out until the trigger simultaneously turns it
on and starts the sweep. For single sweep operation a
mechanical contact or hand key can be connected be
tween the TRIGGER INPUT binding post and ground.
If repeated sweeps occur due to intermittent or bouncing
contact, a capacitor of .1 mf. to 1 mf. should be con
nected across the contact. This capacitor is charged
through 22 megohms and the long time constant pre
vents an immediate recurrence of the sweep.
Sweep Magnifier
Frequently it is desirable to examine in some detail
a portion of the waveshape under observation, for in
stance the rate of fall of the end of a fairly long pulse.
In the Type 511-A the sweep magnifier circuit makes it
possible to expand any desired 20% of the sweep to
cover the entire tube face. When the SWEEP MAGNI
FIER POSITION control is moved from the OUT position,
the sweep is delayed for a variable time and then goes
at about 5 times its normal rate. The operating pro
cedure is to turn the SWEEP MAGNIFIER POSITION to
OUT. Adjust the sweep speed controls so that the por
tion of the wave to be magnified is at the right side of
the tube. Now turn the SWEEP MAGNIFIER POSITION
knob clockwise until the desired signal moves in from
the right to the center of the tube face. The magnified
sweep is not linear over its entire trace so that it is de
sirable to use only the center two inches if possible. If
higher magnification than five is wanted it is only neces
sary to change R47 to a larger value. A value of 10 K
will give a magnification of about 10. The somewhat
lower value chosen appears to be a more usable value
in most cases.
NOTE — A sweep of 10 cm per microsecond
is about the limit of the sweep amplifiers,
so that care must be taken that the magni
fied sweep does not exceed this value.
Ext Sweep Input
Provision has been made for the connection of ex
ternal sweep generators to the Type 51 1A. This might
be a sine wave oscillator for frequency comparison, the
sweep obtained from a "Frequency sweep" signal gen
erator, etc., or an auxiliary slow sweep generator. The
EXT. SWEEP INPUT binding post is connected to the
horizontal deflection plates via the EXT. SWEEP ATTEN.
and a one stage push pull amplifier. The entire system
is DC coupled, permitting the use of very slow sweeps.
TYPE 511-A, 511-AD
SECTION 2, PAGE 2

With the EXT. SWEEP ATTEN. fully clockwise the de
flection sensitivity is approximately 1.5 volts per cm DC
or peak to peak AC.
VERTICAL DEFLECTION SYSTEM
The Type 511 A is equipped with a very flexible ver
tical deflection system capable of amplifying or attenu
ating as necessary a wide range of waveshapes. Since
the best amplifiers and attenuators have faults, it ap
peared undesirable to first attenuate large signals and
then amplify them back to something like their original
size. It was therefore decided that the Type 511 A should
have a switching system so that only as much amplifi
cation as needed to get a reasonably sized image would
be employed. This switch called the INPUT CHAN.
SEL. has four positions, DC, VIA COND, 1 STAGE and 2
STAGES. In the DC position the SIGNAL INPUT con
nector is connected via the INPUT ATTENUATOR to the
upper deflection plate without a coupling capacitor.
The lower plate is connected to the VERT. POSITION
control and bypassed for signals. The VIA COND. posi
tion is similar to the DC except a .1 mfd capacitor is in
series with the deflection plate. On these two positions
the deflection sensitivity is approximately 27 V per cm
DC or peak to peak AC, with the attenuator in the X 1
position.
Normally, connection to the SIGNAL INPUT is accom
plished by attaching the Binding Post Adapter, which is
supplied, and a single lead. When reduced loading on
the circuit under test is desired, the Input Probe should
be used.
CAUTION — THE PEAK POTENTIAL AP
PLIED TO THE PROBE SHOULD NOT EX
CEED 600 VOLTS.
Since the probe introduces an attenuation of 10X, it
will be advantageous to employ a common shielded
lead (no attenuation) to prevent pickup of stray fields
when dealing with very low signals, if the additional
circuit loading is permissible. A ground lead to the
equipment under observation should be provided, and
often an earth ground is desirable.
Vertical Amplifier
With the INPUT CHAN. SEL. switch in the 1 STAGE
position the SIGNAL INPUT connector is connected
to the deflection plate via the INPUT ATTENUATOR, a
cathode follower, the VERT. AMPL. ATTEN., and a one
stage push pull amplifier. The VERT. AMPL. ATTEN. is
a 500 ohm potentiometer in the cathode of the cathode
follower, allowing the gain of the amplifier to be con
tinuously adjusted over a range of two to one, thus fill
ing in the INPUT ATTENUATOR steps. Both low and
high frequency compensation is employed to produce
a wide band of uniform amplification. Careful attention
has been paid to the transient response so that square
wave pulses, etc. will be faithfully reproduced. The
amplifiers are adjusted at the factory for optimum tran
sient response rather than flat frequency response. A
much flatter response is obtainable if desired by in
creasing L6, and readjusting L7, L8, L9, and L 10 , but
overshoot will occur on steep wave fronts. With opti
mum transient response, the rise time (10% to 90% of
full amplitude) is .04 microseconds or better. At the low
frequency end of the band, the top of a 10,000 micro
second square pulse will not depart by more than 5%
from flatness. The deflection sensitivity is approximately
2.7 V per cm peak to peak maximum.
CAUTION — CARE MUST BE TAKEN TO
AVOID OVERLOADING THE AMPLI
FIERS. THIS WILL BE AVOIDED IF THE
IMAGE IS NOT ALLOWED TO EXCEED
THE RULED SECTION OF THE GRATI
CULE, WITH THE VERT. POSITION CON
TROL SET SO THAT WITH NO SIGNAL
APPLIED THE SWEEP LINE IS CENTERED.
In the 2 STAGES position a wide band pre-amplifier
stage is inserted between the INPUT ATTENUATOR and
cathode follower. Since the bandwidth and transient
response of the two stage amplifier are inferior to a sin
gle stage amplifier, this position should not be used un
less it is necessary, in order to obtain a sufficiently large
image. Rise time is .05 microseconds. The gain of the
two stage amplifier is about 100, making the maximum
deflection sensitivity approximately .27 V per cm peak
to peak.
The deflection polarity is inverted when the 2 STAGES
position is used, resulting in downward deflection on
the CRT for positive input polarity.
A three position lever type switch mounted at the rear
of the Type 511 -A permits the operating bias on grid No.
1 of V 1 9 to be varied. With the switch set at the center
(normal) position, the bias applied to V 1 9 is equal to
the bias of V 1 8, resulting in balanced operation and
equal upward and downward undistorted deflection of
the trace. For normal operation, the DEFLECTION
POLARITY switch should be in this position.
If it is desired to observe pulses, the switch should be
set in either the upward or downward position, corres
ponding to the deflection of the image on the cathode
ray tube. In the upward position, the bias of V 1 9 is de
creased, resulting in increased output of V 1 9 and de
creased output of V 1 8, thus permitting greater undis
torted upward deflection. These conditions are reversed
when the deflection polarity switch is in the downward
position.
Direct Connection to Deflection Plates
To allow direct connection to the deflection plates
with the lowest capacity, banana jacks are provided on
a panel accessible through an opening in the left side
of the case. By removing the jumpers the internal cir
cuits may be disconnected. The terminal marked Y1 is
the top plate and the one marked X2 is the right plate.
Deflection sensitivity is approximately 27 V DC per cm
on the vertical plates and 32 V per cm on the horizontal.
If positioning control is desired, the jumpers should
be replaced with 1 megohm resistors and a series cou
pling capacitor employed. Unless balanced input is de
sired, the unused deflection plate should be bypassed
to ground.
SECTION 2, PAGE 3
TYPE 511-A, 511-AD

CALIBRATION
While the cathode ray oscilloscope is usually em
ployed only as a qualitative rather than a quantitative
device, it is the only instrument capable of making
many types of voltage and current measurements on
non sinusoidal wave shapes. To aid in this work the
Type 511 A-AD incorporates an internal clipped sine
wave voltage calibrator and associated SIGNAL-CALI-
BRATE switch, allowing the operator to select either
the internal calibrating voltage or a suitable external
source of calibrating voltage to substitute for the signal
being measured.
Signal Calibrate Switch
This switch permits the vertical deflection system of
the oscilloscope to be conveniently changed from the
SIGNAL INPUT connector to two different sources of
calibrating voltages. In the EXT. CAL. position it is con
nected to the binding post marked CAL. INPUT, which
in turn may be connected to a source of known voltage.
In the remaining six positions it is connected to the
center arm of the CAL. VOLTAGE potentiometer mak
ing available the internal clipped sine wave source of
voltage at power line frequency in six continuously
variable ranges. These six ranges furnish the following
peak to peak voltages: 0-.3, 0-1, 0-3,0-10, 0-30, 0-100 v.,
and are accurate with ±3% of full scale for line volt
ages from 105 to 125 v.
The CAL. INPUT binding post may be used as an
auxiliary signal input. This connection is not recom
mended for observing high speed transients, due to the
slightly greater capacity.
Measurement of Signal Amplitudes
To measure the amplitude of any signal under ob
servation, adjust the size of the image to correspond to
a convenient pair of horizontal lines on the graticule.
Move the SIGNAL CALIBRATE switch to the appropriate
source of calibration voltage and adjust its output until
the image matches the same graticule lines to which
the signal had been previously set. The calibration volt
age is now equal to the signal amplitude.
CAUTION — IF THE INPUT PROBE ( ATTEN.
10X) IS USED, THE SIGNAL AMPLITUDE
IS EQUAL TO TEN TIMES THE CALIBRA
TION VOLTAGE.
The scale on the CAL. VOLTAGE potentiometer is
calibrated in peak to peak volts. If a sine wave is being
measured, this may be converted to R.M.S. by dividing
by 2.828.
CAUTION- DO NOT OVERLOAD THE
AMPLIFIERS WHEN MAKING AMPLI
TUDE MEASUREMENTS.
Another method which is less accurate but more rapid
is to calibrate the oscilloscope itself. Select a suitable
convenient voltage in the range needed, for example
10 volts, and adjust the VERT. AMPL. ATTEN. until a
convenient deflection, say 5 scale divisions, is obtained.
The sensitivity is now 2 volts per division and ampli
tudes may be read directly. The range may be extended
if desired by the INPUT ATTENUATOR and probe which
has an attenuation of 10X.
CAUTION — THE DEFLECTION POLARITY
SWITCH MUST BE IN THE NORMAL
(CENTER) POSITION DURING CALIBRA
TION TO PREVENT ERROR IN THE INDI
CATED AMPLITUDE.
INTENSITY MODULATION (Z AXIS)
If desired, signals may be impressed on the cathode
of the cathode ray tube thus modulating its brightness.
The CRT CATHODE binding post is connected to the
cathode via a .1 mfd capacitor. The cathode resistor
is 120 K. Since the time constant is only .012 sec. long,
square pulses cannot be transmitted without some loss
of shape. Its primary purpose, however, is to transmit
short pulses such as timemarkers, etc.
SWEEP OUTPUT
The SWEEP OUTPUT binding post makes available
the waveshape appearing on the plate of the sweep
generator tube. V 1 0 is used as a cathode follower to
isolate the sweep generator from whatever is connected
to the SWEEP OUTPUT post. The amplitude is approxi
mately 20 V peak to peak.
GATE OUTPUTS
V8 is used as a phase splitter to provide positive and
negative square waves of the same duration as the
sweep. The + GATE is taken from the cathode and DC
coupled, thus providing an accurately square topped
pulse even at the longest sweep times. The — GATE is
taken from the plate via a .05 mfd capacitor to remove
the DC component.
TYPE 511-A, 511-AD SECTION 2, PAGE 4

270
180
120
60
DEGREES
OF
PHASE
SHIFT
FREQUENCY
TEKTRONIX JNC .
12-28-50

SECTION III
CIRCUIT DESCRIPTION
CATHODE RAY TUBE CIRCUIT
The Type 511 A uses a type 5CP1A cathode ray tube.
This tube has a five inch screen and utilizes electro
static focus and deflection. A post-accelerating elec
trode (intensifier) is used to provide increased bright
ness. The total accelerating potential is about 3000 V,
giving a sharp bright image visible in normal room
light.
The various negative voltages necessary to operate
the tube are obtained from a voltage divider network
across the — 1500 V supply. R142 provides the bias volt
age which controls the beam current and thereby image
brightness. This control is labeled INTENSITY. C60
serves to bypass the cathode to ground via the filter
capacitor C 77 in the power supply. In order to bring
the electron beam to a sharp focus at the screen, the
potential of the second anode is adjusted by the FOCUS
potentiometer R140. The ASTIGMATISM control is the
potentiometer R 135 connected between the +225 V and
— 140 V supplies. This control adjusts the potential of
the second anode so that good focus is obtained on
both horizontal and vertical lines simultaneously. In
order to transmit unblanking pulses to the grid of the
cathode ray tube, the .1 mfd 2000 V capacitor C58 is
used. A similar capacitor C59 is used to transmit ex
ternal impulses such as timing markers from the CRT
CATHODE binding post.
The twin potentiometers R131A and R131B provide a
means of varying the average potentials of the vertical
deflection plates and therefore vary the position of the
image. These potentiometers are connected between
the +225 V and — 140 V supplies so that as one plate
is made more negative the other is made an equal
amount positive. By this means the average potential
of the vertical plates is not changed by adjustment of
the VERT. POSITION control. This is essential in order
to maintain good focus over a wide area of the screen.
When the DIRECT position of the INPUT CHAN. SEL.
switch is used, the VERT. POSITION control adjusts the
potential of the lower plate only. In this case it may be
found necessary to adjust the ASTIGMATISM control to
obtain the best focus.
SWEEP CIRCUITS
The sweep chassis contains the circuits necessary to
deflect the electron beam horizontally across the screen
at a uniform rate, starting each sweep in synchronism
with the trigger impulses. Circuits are provided which
cut off the beam between sweeps. Provision is made to
feed various sweep circuit waveforms to binding posts
for external use.
Trigger Phase Splitter
The TRIGGER SEL. switch, operating in conjunction
with VI, the trigger phase splitter, selects the source of
trigger signal and reverses its phase if necessary. The
trigger amplifier V2 requires a positive impulse on its
grid to provide the correct trigger to the multivibrator.
When the TRIGGER SEL. switch is in the — INT. or
+EXT. positions, signals are taken off the cathode of
VI and do not change in polarity. Therefore a positive
impulse must be supplied by the external source or
vertical amplifier as the case may be. With the TRIGGER
SEL. in the -[-INT. or — EXT. positions, signals are taken
off the plate and reversed in polarity, thus providing the
required positive output from negative trigger sources.
Trigger Amplifier
The 6AG7 tube V2 serves to amplify and invert the
positive trigger impulses received from V 1 . The TRIG
GER AMPL. potentiometer R6 varies the bias and thus
controls the point on the positive trigger waveform at
which V2 begins to conduct. R12 in conjunction with
C4A furnishes the small amount of cathode bias neces
sary when the TRIGGER AMPL. potentiometer is op
erated in its extreme clockwise position.
Trigger Coupling Diode
The negative trigger impulses from the plate of V2
are impressed on the plate of V4 by means of the coup
ling diode V3. The diode is used in preference to a
coupling capacitor because it disconnects the trigger
amplifier from the multivibrator once the multivibrator
is triggered. When the multivibrator is triggered the
plate of V4 falls, making the diode plate negative with
respect to its cathode and therefore non-conducting.
This condition is maintained until the multivibrator com
pletes its cycle and is ready to be triggered again.
Multivibrator
To convert the various shapes of trigger impulses
into square waves of controllable duration, suitable for
operating the sweep generator and unblanking the cath
ode ray tube, a multivibrator is provided. This consists
of two tubes V4 and V5. During the waiting period V5
is fully conducting since its grid is at cathode potential
and therefore its plate is held at a low value due to the
voltage drop in R23. With V5 in this condition and the
SWEEP STABILITY correctly adjusted, the grid of V4 is
held well below the cut-off by the voltage divider R17
and R18. The circuit remains in this condition until a
trigger impulse is received. The plate of V4 is driven
down by the trigger pulse and also the grid of V5, be
cause of the coupling capacitor C7. The plate of V5
therefore rises carrying with it the grid of V4 causing it
to conduct. This action continues until V4 is conducting
and V5 cut off. This condition is maintained until the
capacitor C7 discharges, raising the grid voltage of V5
to such a point that it starts to conduct. This makes the
plate of V5 fall, carrying with it the grid of V4 and start
ing a regenerative cycle which ends with V5 con
ducting and V4 cut off, the condition which existed be
fore the trigger impulse occurred. Thus the plate of V4
produces a square negative pulse and simultaneously
the plate of V5 produces a positive pulse. The negative
pulse is used to control the operation of the sweep gen
erator and the unblanking of the cathode ray tube. The
positive pulse is used to furnish the plus and minus
SECTION 3, PAGE 1
TYPE 511-A, 511-AD

GATE voltages available at the front panel binding
posts. The duration of the time V5 is cut off is deter
mined by the time constant of C7, R20C, R20C1 thru
R20C9 (depending upon the position of S10A), and the
voltage applied across the circuit and is substantially
independent of the characteristics of the trigger im
pulse. To cover a range of sweep time from .1 sec. to
1 microsecond, C7 has five values as selected by the
SWEEP RANGE switch. The calibrated variable resistor
R20C is returned to +225 volts. This makes possible the
use of a larger value of C7 than would otherwise be
possible, thus reducing the voltage divider action of the
stray capacitances to ground in the grid circuit of V5.
Variation of R20C, R20C1-9, in conjunction with the five
values of C7 gives a continuously variable adjustment
of multivibrator pulse length.
Unblanking Circuit
During the waiting period the bias on the cathode ray
tube is such that it is completely cut off. As soon as a
trigger appears and the sweep starts, it is necessary to
provide a positive pulse on the grid of the cathode ray
tube and thus turn on the electron beam. This pulse
should have an extremely fast rise and a very flat top
so that the brightness of the image is uniform. To
secure a pulse of this nature, the negative pulse from
the grid of V5 is limited by plate current cutoff in
V7.1A before it reaches full amplitude. The voltage
divider R37, R38 sets the d.c. bias on the grid of V7.1A
at approximately 0 volts and supplies a negative pulse
of 45 volts amplitude. Cl 2 insures that the leading edge
will be coupled thru without loss of rise time due to grid
and wiring capacities to ground. The 45 volt negative
pulse is more than adequate to drive V7.1A into cutoff,
thus producing at the plate a square, flat topped posi
tive pulse having an amplitude of 80 volts. To provide
increased rise time, L2.1 is employed in the plate circuit
of V7.1A. The cathode follower V7.1B serves to isolate
the plate circuit of V7.1A from the capacity to ground
of the cathode ray tube grid and associated wiring, thus
preventing any appreciable reduction in rise time due
to their effect. This circuit is capable of unblanking the
tube in less than .1 microsecond after a sharp trigger
pulse reaches the TRIGGER INPUT binding post.
Gate Output Generator
V8 serves to isolate the gate output binding posts from
the multivibrator. It receives a positive pulse on its grid
of the same duration as the sweep from the plate of V5
via the voltage divider R32 and R33. C 10 maintains the
steep sides of the pulse. Since the plate and cathode
load resistors are equal, pulses of equal size but oppo
site polarity appear at the plate and cathode. The
+gate from the cathode has no blocking capacitor and
therefore preserves the square pulse for the longest
sweeps. It was not felt desirable to have the — Gate
binding post carry the +225 V potential of the plate;
therefore a blocking capacitor is used.
Sweep Generator
The sweep generator circuit produces the basic wave
necessary to sweep the beam linearly across the tube
and return it to its starting point. During the waiting
period the 6AG7 tube V9 is held fully conducting since
it has no bias and therefore its plate is about at ground
potential. When a trigger occurs the negative pulse
from the multivibrator cuts the grid of V9 off very rapidly.
The plate therefore rises in exponential fashion at a
rate depending upon R20D, R20D1-9 (as determined by
setting of S 10 B), R39, the voltage applied across the
circuit, and Cl 5. When the multivibrator pulse ends
V9 conducts again, thus discharging C 1 5. Since C 1 5 is
charged to only about 5% of the supply voltage the
rate of rise is very nearly linear. Five values of C 1 5 as
determined by the SWEEP RANGE switch in combina
tion with the variable resistors R20D and R20D1-9 pro
vide a continuous variation of sweep speed of from .1
sec. to 1 microsecond for a 10 cm sweep. In order to
maintain the correct multivibrator pulse length as the
sweep speed is increased, the SWEEP RANGE switch
changes C7 in the multivibrator and C 15 simultaneous
ly. In a like manner the SWEEP SPEED MULT, controls
are dual controls changing R20C, R20D and R20C1-9,
R20D1-9 simultaneously. In order to maintain the cali
bration of the SWEEP SPEED MULT, dials when tubes
are changed, etc., the voltage applied to R20D may be
varied by R42 which sets the grid potential of the cath
ode follower VI 5. The use of the cathode follower in
stead of a potentiometer maintains a constant charging
potential as R20D, R20D1-9 is varied. Details of this
adjustment may be found in Section IV. The two resistors
R39. 11 and R39.12 connected in series are shunted
across R20D1-9 to compensate for the plate circuit
loads of V9.
Sweep Output Cathode Follower
To provide the necessary isolation between capaci
ties fastened to the SWEEP OUTPUT binding post and
the sweep generator, the cathode follower V 1 0 is pro
vided. The grid of V 1 0 is connected to the plate of the
sweep generator. The SWEEP OUTPUT binding post is
connected to the cathode of V 10 without a blocking
capacitor.
Sweep Magnifier
The function of this circuit is to delay the start of the
sweep for a variable time, and then cause it to go at
five times its normal speed. This is accomplished by
the biased cathode coupled amplifier V11 . In this type
of amplifier a positive change in the grid potential of
V 11A raises both cathodes and therefore corresponds to
a negative change on the grid of V 11 B. Thus the plate
of V 11 gives an amplified version of the signal on the
grid of V 11 A, without change of polarity. The SWEEP
MAGNIFIER POSITION potentiometer raises the poten
tial on the grid of V 11 B above ground and thus the cath
ode potential of V 11 A. No sweep appears on the plate
of V 11 B until the plate of the sweep generator overcomes
this bias, then the amplified sweep appears. Sufficient
bias is available on the SWEEP MAGNIFIER POSITION
to make it possible to start the magnified sweep at any
point on the normal sweep. V6 is employed as a DC
restorer to insure that the magnified sweep will start at
the same potential each time, thus preventing jitter or
instability of the trace. When the magnified sweep is
not desired, the SWEEP MAGNIFIER POSITION knob
TYPE 511-A, 51 1-AD
SECTION 3, PAGE 2

is turned to the OUT position which operates a SPDT
switch connecting the sweep amplifier directly to the
plate of the sweep generator.
Sweep Amplifier
The sweep voltage at the plate of V9 is only about
20 V amplitude. To sweep the spot across the screen,
about 350 V is necessary. The sweep amplifier provides
the necessary amplification and in addition converts
the single sided voltage from the sweep generator into
a balanced voltage suitable for deflecting the beam.
This balanced voltage is necessary to maintain the aver
age potential of the deflection plates constant over the
entire sweep, and thus prevent defocussing. The am
plifier which does this uses a cathode coupled circuit
consisting of the triode connected 6AU6 tubes V13 and
V 1 4. The action of this circuit is the same as described
for the sweep magnifier except that load resistors are
present in both plates. The HOR. POSITION control
varies the bias on V14 and thus determines the position
from which the sweep starts. To insure that the sweep
will always start at the same point on the screen each
time (at a given setting of the HOR. POSITION control),
the 6AL5 restorer diode V 12 is connected between the
grid of V 1 3 and ground. This diode removes any charge
which C20 may have gained during the sweep.
High frequency compensation provides sufficient
band width to amplify the 1 microsecond sweep with
good linearity.
This is accomplished by the bypassing effect of C22,
which at high frequencies reduces the degeneration in
troduced in the cathode circuit by R65 and R66. Addi
tional compensation is provided by the inductance of
R69 and R63.
When the SWEEP RANGE switch is on the EXT. posi
tion, the input to the sweep amplifier is shifted from the
sweep generator to the arm of the EXT. SWEEP ATTEN.
potentiometer.
To obtain good focus on a cathode ray tube, it is nec
essary that the final anode and both pairs of deflection
plates have approximately the same average potential.
Since it is necessary to have the vertical plates at
ground potential so that a direct connection can be
made, the average potential of the horizontal plates must
also be near ground. The mean potential of the sweep
amplifier plates is about + 250 V. This is moved down
to ground by means of the group of neon glow lamps.
A steady current of about 200 microamperes keeps them
ionized so that any changes in the plate potentials of
the sweep amplifiers appear on the deflection plates
unchanged in amplitudes, but moved down 250 V. The
biasing current is obtained from the — 1500 V cathode
ray power supply via the voltage dropping resistors
R153 and R154. Since the impedance of the neon glow
lamps is rather high at frequencies involved in the fast
est sweeps, C24 and C25 are shunted across them to
transmit these frequencies.
VERTICAL DEFLECTION SYSTEM
The vertical deflection system provides the means of
attenuating or amplifying input signal amplitudes so
that they may present a convenient image on the cath
ode ray tube. Signals may be attenuated as much as
8 times or amplified as much as 100 times without ap
preciable change in shape.
Probe
A frequency compensated signal input probe is sup
plied to provide reduced loading on the circuit under
observation. It consists of a 9 megohm series resistor
paralleled with a compensating capacitor, and provides
an input impedance of 10 megohms shunted by 14 mmfd.
CAUTION — ALTHOUGH THE PROBE IN
TRODUCES A SIGNAL ATTENUATION
OF 10 TIMES, IT SHOULD NOT BE CON
NECTED TO CIRCUITS WITH PEAK VOLT
AGES EXCEEDING 600 VOLTS.
Input Attenuator
All signals and calibrating voltages pass through a
four position, RC compensated attenuator having at
tenuation ratios of 1, 2, 4 and 8. If a conventional resis
tance voltage divider is shunted by capacitors whose
values bear the inverse ratio to the resistor values, the
attenuation is independent of frequency. The attenuator
is designed to have an input resistance of 1 meg shunted
by 40 mmfd for all positions. Since the input circuits to
the amplifiers and deflection plate are arranged to pre
sent 1 meg shunted by 40 mmfd, the values chosen for
the attenuator are such that correct operation is obtained
when these values are in parallel with the shunt arm.
The capacitors C32, C35, and C38 shunted across the
attenuators have no effect on the attenuation ratio but
are adjusted so as to keep the input capacity at 40 mmfd.
Vertical Amplifier
The Type 511 A contains a wide range two stage ver
tical amplifier with a switching arrangement so that
only one stage may be used if desired. The first stage
which is used only in the 2 STAGES position of the IN
PUT CHAN. SEL. switch uses a 6AG7 tube V 1 6.
The output stage is a cathode coupled, push-pull
6AG7 stage, providing approximately 110 V of undis
torted output. The operation of this stage is the same as
that of the sweep amplifier stage. The use of a push pull
stage is required to give sufficient output and maintain
the average potential of the deflection plates constant
so as to prevent defocussing the beam. Low frequency
compensation is provided to correct for the effect of the
coupling capacitors. The resistors R110 and R125 along
with the capacitors C51A and C51B provide a rising
low frequency characteristic together with a phase cor
rection. To take up variations in the component values,
the grid resistor R1 16 is made adjustable. The procedure
for this adjustment is given in Section IV. The induct
ances, L7, L8, L9 and L10 provide the high frequency
compensation. A four terminal coupling network is
used to give the greatest possible bandwidth. Every
SECTION 3, PAGE 3
TYPE 511-A, 511-AD

precaution has been taken to obtain the smallest stray
capacities consistent with good mechanical construc
tion.
To increase the undistorted deflection when observ
ing pulses of a particular polarity, provision is made to
move the operating point of the push-pull output am
plifier from its normal position to one which allows al
most the entire output swing to be utilized in either one
direction or the other.
The DEFLECTION POLARITY switch, S9, permits the
operating bias on grid No. 1 of V 1 9 to be varied. With
the switch set at the center (normal) position, the bias
applied to V19 is equal to the bias of V18, resulting in
balanced operation and equal upward and downward
undistorted deflection of the trace.
In the upward position, the bias of V 1 9 is decreased,
resulting in increased output of V 1 9 and decreased out
put of V 1 8, thus permitting greater undistorted upward
deflection. These conditions are reversed when the de
flection polarity switch is in the downward position.
The 6AG7 cathode follower V17 serves primarily as
an impedance transformer so that a low resistance po
tentiometer can be used as a gain control. It is neces
sary that the potentiometer have a low value so that
stray capacities do not appreciably vary the frequency
response as the control is varied. To prevent overload
ing the cathode follower, the VERT. AMPL. ATTEN. has
a stop limiting its attenuation to a maximum of 2. This
is sufficient to cover the steps of the INPUT ATTENUA
TOR. The coupling capacitor C49 serves to remove
the DC component from the VERT. AMPL. ATTEN. so
that the image does not jump around if the control is
moved suddenly. Another function of the cathode fol
lower is to permit the insertion of a delay network in the
video amplifier. The chassis of the Type 511 A is drilled
to permit the insertion of a Tektronix Type 1AD25 Delay
Network. This delays the signals .25 microseconds with
out appreciable distortion. A panel switch permits the
removal of the delay when desired. When the delay
network is factory installed, the oscilloscope is desig
nated as Type 511 AD.
When the INPUT CHAN. SEL. switch is in the 2
STAGES position, the 6AG7 pre-amplifier V 1 6 is in the
circuit. This stage employs the same compensation
system as the output amplifier. Variable resistor R99
controls the low frequency response, and L4 and L5
the high frequency response. The negative bias from
the voltage divider R90 and R91 places the tube on the
correct portion of its operating curve. So that the screen
dissipation will not be excessive, the screen voltage is
supplied through R95. C45A keeps the potential rela
tively constant when signals are applied to the control
grid.
CALIBRATING CIRCUITS
CAUTION — THE SCALES OF THE CAL.
VOLTAGE CONTROL INDICATE PEAK
TO PEAK VOLTS, NOT RMS. MULTIPLY
RMS BY 2.828 TO CONVERT TO PEAK TO
PEAK.
The calibrator waveform is derived from the line fre
quency voltage of a 280 volt T1 secondary winding.
The positive peak is clipped (limited) by the diode
connected section of a 12AT7, V 1 6.1. The point of limit
ing is determined by the setting of the CAL. ADJ. poten
tiometer R75.4. Since the voltage across R75.4 is ob
tained from the +225 volt regulated supply, the point
of limiting is not affected by line voltage variations from
105 to 125 volts, thus the accuracy of the output voltage
is held within ±3% of full scale for these line voltage
variations. This limited waveform is applied to the
cathode follower section of V 1 6.1 which clips the nega
tive peak and provides six ranges of calibrating voltage
by employing a six step precision voltage divider as the
cathode follower load. Continuously variable output
voltage from each range is obtained from the CAL.
VOLTAGE potentiometer which may be connected to
any one of the six steps of the precision voltage divider.
CAUTION — DO NOT ATTEMPT TO
CHECK THE CALIBRATOR ACCURACY
WITH AN A.C. VOLTMETER. IF INACUR-
ACY IS SUSPECTED, THE OUTPUT
SHOULD BE CHECKED BY THE COM
PARISON METHOD. REFER TO SECTION
4, ADJUSTMENT OF CALIBRATOR VOLT
AGE, FOR PROPER PROCEDURE.
The SIGNAL-CALIBRATE switch S3.1, permits selec
tion of the SIGNAL INPUT, CAL. INPUT (which may be
used as an alternate signal input), or any one of the
six calibrating ranges from .3 v. to 100 v. peak to peak.
Refer to Section 2 "CALIBRATION," for operating in
structions.
POWER SUPPLY
In order to make the operation of the Type 511 A
independent of line voltage variations over the range
of 105 to 125 volts, all DC power supplies are electroni
cally regulated. The accelerating potential for the CRT
is obtained from an oscillator operating from the regu
lated +225 v. supply. A single transformer supplies
all of the 60 cycle power.
The principal power supply provides +225 v. at
approximately 250 ma. Two 5V4G tubes are used as
rectifiers. The comparatively low voltage drop of these
tubes reduces the no load voltage to which the input
capacitors may be subjected. A large input capacitor,
80 mfd., reduces the ripple to about 12 volts. The elec
tronic regulator reduces this to less than .1 volts. This
circuit consists of V27, V28, V29 and their associated
components. To see how this circuit works, consider
what happens when the output voltage at the cathode of
V27 increases for any reason. The cathode of V28 is
held at a constant potential by the type 5651 voltage
reference tube V29. An increase of voltage at the cath
ode of V27 increases the grid voltage of V28, thereby
decreasing its plate voltage and consequently increas
ing the grid bias on V27. An increase in this bias
increases the voltage drop across V27 and thus de
creases the output voltage. If a decrease in line voltage
and increase in load current tend to decrease the out
TYPE 511-A, 511-AD
SECTION 3, PAGE 4

put of the regulator, the reverse action takes place.
Thus an equilibrium is reached where the regulated
output voltage is held constant within very narrow
limits. To improve the action of the regulator for ripple
or sudden changes of load, the capacitor C70 couples
the grid of V28 directly to the output. The potentiometer
R159 allows adjustment of the output voltage to 225
volts when the tubes are changed, etc.
A 6X4 rectifier V24 with its cathode connected to one
side of the high voltage winding, supplies a negative
voltage of approximately 300 volts. The plates of V24
are tied together since it is used as a half wave recti
fier. C68 is used as the input capacitor. To provide
regulation and additional filtering, the gas filled regu
lator V30 is used. The 470 ohm resistor in series with
the output of V30 eliminates a tendency of V30 and C21
(on the sweep chassis) to form a relaxation oscillator.
The +450 volts necessary to operate the sweep ampli
fier is obtained from the full wave rectifier V21 whose
output voltage is added to the output of the main recti
fier. To obtain regulation and filtering, a regulator
consisting of V25 and V26 is used. This regulator oper
ates in the same manner as the +225 supply, using
the regulated +225 as reference voltage. Thus, if the
+225 is not set ats its correct value, the +450 volt output
will also be in error.
In order to provide the + and — 1500 volts neces
sary to operate the CRT, an oscillator type supply is
used. Since the input power to the oscillator comes
from the regulated +225 volts, its output is not affected
by line voltage changes. The oscillator uses the 6AQ5
tube V31 in a conventional Hartley circuit. A high volt
age secondary on the oscillator transformer supplies
approximately 1250 V RMS to the two type 1B3GT/8016
rectifiers V32 and V33. Filament voltages for these
tubes are obtained from windings on the oscillator trans
former. Since the frequency of the oscillator is fairly
high (2 KC), a single .05 capacitor provides adequate
filtering for the +1500 volts. A filter consisting of a .05
mf. input capacitor, a 27K resistor, and a .5 mf. output
capacitor is used on the — 1500 volt supply because of
the increased load and need for an adequate bypass on
the CRT cathode. A variable resistor R165.2, in series
with the oscillator screen supply, provides adjustment
of the — 1500 volt supply to compensate for tube
changes, etc. Procedure for setting this adjustment
may be found in Section IV.
SECTION 3, PAGE 5
TYPE 511-A, 511-AD