[Amps] What am I missing?

[Tom W8JI]

> 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