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The signal should not be heard at
any of these points.
The function of a screen-grid is
two-fold:
- To shield other electrodes.
- To influence the operating characteristics of the tube.
By reason of its shielding effect the
screen-grid prevents interaction between
plate and grid. As far as a.c.
is concerned, the screen is grounded
through the screen by-pass condenser.
Normally no a.c. or signal voltage
should appear on the screen.
The d.c. voltages can be checked with
a voltmeter.
Trouble
Signal or hum usually indicates insufficient
by-passing, open paper condenser, or
dried-out electrolytic.
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