Part of the problem is that not everyone agrees what Q is. The classic
engineering definition of Q in an oscillating system is a ratio of stored
energy to the energy dissipated per cycle. In a pi network this is composed
of two parts. Think of the pi as two back to back L networks. Each one
contributes to Q. In the usual tube amp case, the impedance ratio is large
and Q is on the order of 10. Under those conditions, the total Q is
dominated by the input side, resulting in a convenient approximation. In
other cases, you can have a considerable discrepancy. Elmer Wingfield,
W5FD, wrote it up nicely in the Aug 1983 QST.
73, Carl WS7L
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