View the L-network as a parallel LC with the load Rs in series with the L.
At resonance this circuit is equivalent to a parallel LCRp (all in
parallel) with the
Rp equal to (X^2)/Rs . The Q is always in this case equal to the square
root of the ratio of Rs ( the load)
and Rp which should match the output impedance of the tube.
So if you have a plate impedance of 5000 and an output impedance of 50 the
Q must be
10 to match the two. This makes sense because for the same power 10 times
the current must flow
thru 50 ohms as thru 5000 ohms. And the circulating current, all of which
flows thru Rs(the load)
is Q times the input current applied to the junction of C and L.
A L-network should be used to match large plate and load resistance ratios
if you want a reasonable Q.
In some cases reactances are not equal and those are when matching a
impedance that has a reactive component
such as a short antenna. Some of the output reactance is used to
cancel out the reactive component of the antenna.
Otherwise the rest of the circuit should resonant.
73
Bill wa4lav
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