c. Video Amplifier. The video amplifier circuit (figure 6) consists of
two amplifiers with three transistors each and feedback and drift
compensation for gain stability. Feedback is provided by the RC combination
of R5, C4, R13, C11 and transistors Q3 and Q6. Drift compensation is also
accomplished with the addition of Q3 and Q6. Positive feedback to amplifier
no. 2 from the output amplifier increases amplifier no. 2 gain at higher
frequencies.
The addition of Q3 and Q6 in the feedback loops of the two amplifiers
provides three functions: 1) act as negative feedback amplifiers to reduce
the gain which reduces any drift caused by temperature changes; 2) maintain
the amplifier gain at low frequencies; and 3) filter ripple on the -14 volt
line in conjunction with C6 and C13.
Figure 6.
d. Output Amplifier. The output amplifier (figure 7) consists of the
output amplifier circuit and the meter circuit.
Emitter follower Q4
provides the amplified input signal to the counter via the rear panel of the
Model 5261A.
This same signal is supplied to the Output 50 ohm jack for
monitoring with an oscilloscope or application to other equipment.
88
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