Re: [Amps] Tuned Input and the MFJ-259B

[Vic Rosenthal <vic@rakefet.com>]

Bill Smith wrote:
> I am using a MFJ-259B to tune up my Tuned Input
> circuits.  I know to go for 1:1 SWR or as close as I
> can get it and 50 ohms of resistance(Rs).  How about
> Xs?  What value am I shooting for?

You probably know this, but the correct way to do it is to temporarily 
put a non-inductive resistor equal to the input impedance of your tubes 
under operating conditions, and do the test with the amplifier powered off.

Then you look for an SWR of 1:1, which should occur when R=50 and X=0. 
That means that your tuned input circuit has transformed the input 
impedance to 50 ohms at the proper frequency.

The trick is finding out the value of the resistor that you need to do 
the test!  Some data sheets show it and some don't.  Calculating this 
value is a topic which has been discussed here and you can probably find 
it in the archives accessible on <http://www.contesting.com>.

Vic K2VCO

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