Lesson 1/Learning Event 3
Learning Event 3:
1. General. The video amplifier performs certain basic functions for the red,
blue, and green signal paths within the camera head. These include: beam set,
sensitivity, clamping, clipping, and distribution of the video signal (fig 14, a
foldout located at the end of Lesson 3).
2. Input First Stage Amplification. Video output from each of the three
preamplifiers is fed to the corresponding video amplifier and terminated into a 75
ohm load. The video signal is sent through an attenuator circuit in order to
establish a typical 2/1 beam reserve ration.
a. From the beam set circuit the video signal is sent to an amplifier stage
where the video gain is set to a predetermined voltage, (manufacturer's technical
b. If the video gain amplifier is a fixed gain type, it is important that
the video gain setting located on the preamplifier board is set to manufacturer's
3. The sensitivity circuitry controls the signal current (fig 14). This is
accomplished by attenuating or padding the video signal. Commonly, there are two
types of sensitivity circuits:
a. The high sensitivity circuit is used when there is a low current signal;
it reduces the attenuation, or resistance, which allows the video signal to proceed
at a higher value.
b. The low sensitivity circuitry is used when too much current is available
in the video signal. When this circuit is engaged, the overall resistance is
increased, which attenuates the signal current and reduces the signal to an
NOTE: When using the sensitivity circuitry you
may change the BEAM DISCHARGE CHARACTERISTICS.
4. Fixed Amplifier. The video signal then is passed to a fixed amplifier (fig 1
4). This is a noninverting amplifier of high stability. The video signal is sent
from this stage to the final stage of the video amplifier for processing.