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Here the signal should reach its
highest level. A gain of 10 to 20 is
normal for pentodes and 2 to 5 for
triodes.
  
The a.c. plate current creates a
strong field around (glass) tubes and
the plate wiring, including the output
transformer. Thus, the signal may be
heard when the probe is merely
brought near to these parts.
Trouble
  
In this part of the circuit, trouble is
easily located. The components are
simple and the input signal is at a high
level. No signal at R may indicate a
defective tube, wrong voltages, open
output transformer primary, break in
wiring, or failure of some other
component. Voltage and continuity tests
give the answer quickly.
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