I don't know how much harmonic attenuation you would get in the matching
network for a solid state 2m PA, but at 500 watts output, it might not be as
much as 30dB, and then you need 40dB from the stubs. So a low pass filter has
its attractions, if only as an additional filtering stage. A valve PA, on the
other hand, is likely to start from a better position in that the harmonics
will be attenuated by the relatively high Q tank circuit.
One has to consider what variety of LPF, too - Butterworth, Tchebycheff or
Cauer-Tchebycheff, although that last one might be a bit impractical at these
frequencies. The variety also affects the cut-off frequency definition.
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