> January QST has an article on old amplifiers that
> advocates replacing the input circuits on an SB-221 with
> simple parallel-tuned circuits for each band. How can
> these circuits possibly achieve matching between a 50-ohm
> exciter and the tubes?
They can't if the impedance of the tubes is anything other
than 50 j something.
A pair of 3-500's is fortunately close to 50 ohms with some
reactance, so the parallel network will work if it is placed
right at the tube. Place it 2 feet away and you have a
problem on 10 and 15 meters.
73 Tom
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