The reason for short-circuiting the harmonic currents in the cathode
circuits
is that they would cause voltage drops over the cathode circuit if not
bypassed.
As the cathode and plate circuits effectively are in series, these
voltage drops
may influence the slope and shape of the plate load line,
depending on their phase and amplitude relationships with the
fundamental current.
This can cause decreased power output and efficiency, in a similar way
as insufficient Q in the plate circuit.
If the impedance of the cathode circuit becomes real at some harmonic
frequencies,
power will also be dissipated in the circuit.
Bill Orr's reommendation of capacitance in the cathode circuit comes
from the
recommendation to have a circuit Q of about 3, and for a 100 ohms
input impedance
the resultant Q in a resonant circuit has this value with a
capacitance of
13 pF/m. Values of around 20 pF/m were used in circuits with lower
input impedances.
73/
Karl-Arne
SM0AOM
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