Tektronix 502 series, Instruction Manual

Page: 32 / 114

HORIZONTAL AMPLIFIER
The Horizontal Amplifier consists of an input
cathode-follower, a cathode-coupled input-ampli­
fier stage, and a plate-loaded output amplifier
to drive the horizontal deflection plates in the
crt.
The HORIZONTAL DISPLAY switch SW331 de­
termines whether the input waveform is received
from the Time-Base Generator or from an ex­
ternal source. When this switch is in either the
NORMAL or the SWEEP MAGNIFIED position,
the waveform is received from the Time-Base
Generator. With this configuration the sweep
sawtooth is coupled to the Input C.F. via the fre­
quency-compensated voltage divider R311-R312.
The Horizontal POSITIONING control R398 sup­
plies a manually adjustable dc voltage to the
grid of the Input C.F. V183B for horizontal posi­
tioning of the crt beam. The Input C.F. isolates
the Miller Circuit from the Horizontal Amplifier
and provides a low-impedance source to drive
the switch capacitances and the Input Amplifier.
The Horizontal Amplifier is controlled by feed­
back networks much the same as the Vertical
Amplifiers. This illustrated in Fig. 4-2. A nega­
tive feedback loop extends from the plate circuit
of the Output Amplifier to the cathode circuit of
the Input Amplifier. The Output Amplifier, on
the other hand, has a positive feedback loop be­
tween the plate circuit on one side and the grid
circuit on the other.
The Input Amplifier is a cathode-coupled para-
phase amplifier, and converts the positive-going
sawtooth voltage, obtained from the Time-Base
Generator, to a push-pull output sawtooth volt­
age. The gain of the Input Amplifier is deter­
mined by the amount of resistance connected be­
tween the two cathodes, which in turn determines
the degree of negative feedback applied to the
stage. In the NORMAL position of the HORI­
ZONTAL DISPLAY switch R331 is not in the cir­
cuit and the cathode resistance is composed of
R334 in parallel with the series combination of
R336, R337 and R338. In any of the SWEEP
MAGNIFIED positions, one of the R331 resistors
is switched into the cathode circuit and shunts
the total cathode resistance to a lower value.
FROM
TIM E-BASE
G E N .
N E G A TIV E FEEDBACK
N E G A TIV E FEEDBACK
Fig. 4 -2 . Block diagram of the Horizontal Amplifier, illustrating the feed­
back loops.
4-8
CIRCUIT DESCRIPTION — TYPE 502