Horizontal Amplifier - Tektronix 221 Instruction Manual

Fig. 4-3. Simplified block diagram of the Horizontal Output Amplifier circuit.

Horizontal Amplifier

The Horizontal Output Amplifier provides amplification
for the sweep signal or the horizontal signal (used in theX-
Y mode), to drive the crt deflection plates. A block diagram
of the Horizontal Output amplifier is shown in Fig. 4-3. The
schematic is shown on diagram 3.
Transistor Q502 is connected as a buffer amplifier
between the sweep generator and the horizontal amplifier.
The horizontal amplifer consists of three operational
amplifiers. Transistors Q516, Q522, and Q526 are con­
nected as the first operational amplifier that controls the
horizontal gain, positioning, and magnification.
Resistors R504 and R505 serve as the input resistance
to the amplifier. The feedback resistance (R525, CR525,
and R511) is connected from the emitter of Q526 back to
the operational amplifier input (emitter Q516), and deter­
mines the gain for the XI and X10 mode. In the XI mode,
Q518 is turned on and shorts R511. In the X I0 mode, Q518
is turned off, adding R511 to the feedback resistance.
Horizontal Position control R518 applies an offset current
to the input of the operational amplifier for the required dc
positioning.
REV. B, AUG 1974
+
I
| HO BIZ MA ]
g
S521
Circuit Description—221 Service
R545
Current output from the collector of Q526, which is
proportional to the output signal, is applied through the
diode limiter CR532, CR533, CR535, and CR536 to the
input of the second operational amplifier.
TransistorsQ532, Q542, and Q544 are connected as the
second operational amplifier, which drives the input
resistance (R548) of the third operational amplifier and the
positive deflection plate. Resistor R545 serves as the
amplifier feedback resistance, with R542 and C542
providing the High Frequency signal path for the positive
going output signal.
The third operational amplifier consists of transistors
Q552, Q554, and Q556, with R548 being the input
resistance and R556 the feedback resistance. It is con­
nected as an inverting amplifier with a gain of one, and
drives the negative deflection plate. This amplifier
operates similarly to the vertical deflection plate drivers
described in the Vertical Amplifier section.
HO RIZSIG
TO CRT
DEFLECTION
PLATES
4-5