Tektronix 5441 Instruction Manual page 39

Theory of Operation-54411~5441
The vertical amplifier provides the final amplification for of feedback resistor R104-R103 or R128-R129 and emitter
the vertical signal before it is applied to the vertical deflec- resistor R111. The networks parallel to the emitter resistor
tion plates of the crt. The vertical amplifier circuitry includes compensate for the signal losses in the delay line. R135 acts
the delay line and part of the beam finder circuit, which re-
as a dc centering control, which compensates for resistive
duces the final drive to compress an over-scanned display tolerance errors and crt electrical center error in the vertical
to within the viewing area of the crt. amplifier, and allows the mainframe input to be
standardized.
Delay Line
The next stage of amplification consists of Q148, Q170,
Delay line DLI 00 provides approximately 140 ns of delay
~ 1 6 5 , and QI 72. Thermistor RTI 57, resistor ~ 1 5 7 , varicap
for the vertical signal. This allows the time-base circuits time
CR146, and capacitor (-160 between the emitters of Q148
to initiate a sweep before the vertical signal reaches the crt
and Q165 comprise a thermal compensation network to
tor-
deflection plates. This delay of the vertical signal allows the
for frequency loss with temperature changes. The t~~
leading edge of the signal originating the trigger pulse to be
RC networks ( ~ 1 51 -CI 56 and RI 55-~153-Cl55) in the
displayed when using internal triggering.
emitters of Q148 and (2165, and the RCL network in the
collectors of Q148 and Q165 provide high-frequency
compensation.
The delay line has a characteristic input impedance of
approximately 75
! J
from side-to-side.
The final amplifier stage consists of Q180, Q188, (2182,
and (2190. R175 provides a means of adjusting the vertical
Amplifier
amplifier gain within a
k
20% range.
The vertical amplifier consists of a high bandpass three-
stage paraphase amplifier having an input sensitivity of ap-
proximately 35 mVldiv and a voltage gain of about 11 5. The
amplifier is differentially driven at the bases of QlOO and
Q125 by the input signal from the delay line. R l 00 and R125
terminate the delay line.
The first amplifier stage consists of Q100, Q106, (2125,
and (2130. The gain of this stage is determined by the ratio
Pushing the BEAM FINDER switch compresses an off-
screen display to determine its location. This is accom-
plished by turning off Q140, when the BEAM FINDER
switch is pushed, which reduces the standing current in the
second amplifier stage. This lowers the voltage drop across
R172 and R176, which lowers the standing current in the
final amplifier stage. The lower final amplifier stage standing
current reduces the possible scan on the crt.
REV MAY 1982