Circuit Description; Cathode-Ray Tube Circuit - Tektronix 511 Instruction Manual

Major circuit number changes and improvements occurred in
the Type 511 Oscilloscope starting with S/N 455. At this time the
Type 511 designation changed to Type 511A. Numbers in paren­
thesis indicate the earlier values. If your oscilloscope has a se r­
ial number between 101 and 454, please use the part number in
parenthesis. For greater clarity and convenience to you, it may
be desirable to cross out all of those part numbers and text s e c ­
tions which do not apply to your particular Tektronix instrument.
The Type 511A uses a type 5CP1A (101-
5099) or 5ABP (5100 and up) cathode-ray
tube. This tube has a five inch screen and
utilizes electrostatic focus and deflection. A
post-accelerating electrode (intensifier) is used
to provide increased brightness.
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
R142 provides the bias voltage which controls
the beam current and thereby image bright­
ness. This control is labeled INTENSITY. C60
serves to bypass the cathode to ground via the
filter capacitor C77 (C69) 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 poten­
tiometer R135 connected between the +225 v
(+125 v) and -140 v supplies. This control adjusts
the potential of the second anode so that good
focus is obtained on both horizontal and verti­
The sweep chassis contains the circuits
necessary to deflect the electron beam hori­
zontally 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.

CIRCUIT DESCRIPTION

CATHODE-RAY TUBE CIRCUITS
cal lines simultaneously. In order to transmit
unblanking pulses to the grid of the cathode-ray
tube, the .1 pf, 2000 v capacitor, C58 is used.
A similar capacitor, C59, is used to transmit
external impulses such as timing markers from
The total the CRT CATHODE binding post.
provide a means of varying the average poten­
tials of the vertical deflection plates and there­
fore vary the position of the image. These
potentiometers are connected between the + 225 v
-1500 v supply.
(+125 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 aver­
age 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 con­
trol 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
Trigger Phase Splitter
junction 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.
T Y P E 5 t f —C l R C U I T
SECTION 3
The twin potentiometers, R131A and R131B,
The TRIGGER SEL. switch, operating in con­
D E S C R I P T I O N
P A G E 3 - 1