[Amps] amp input circuit...

Roy royanjoy at ncn.net
Thu Oct 23 13:25:23 EDT 2008


"...The 4-1000 has a generally accepted input impedence of 100 ohms.  So I 
planning on using a 2:1 step up unbalanced to unbalanced balun followed by
a parallel tuned circuit, Q of 2-3, for each band.  Taking this approach I
will need only one relay contact per band to switch each tuned circuit (as
opposed to two needed to switch a pi network)...(etc.)"

Such is not considered good practice. Only partial conductance of  RF cycles 
exist in that stage. There is a good reason for manufacturers to go to all 
the trouble and expense of using pi-nets. Pi-nets restore the full cycles 
through their flywheel effect. The output cap of the pi-net also by-passes 
the cathodes to ground, improving stability, and should be located 
physically very close to the cathode connection.

73,    Roy,           K6XK

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