[AMPS] Tuned Input Circuit Q

[2]

>
>> //  The statement that  "or a parallel tuned network"  should be
>> questioned.  A parallel tuned input will work ok only when the Q
>> requirement is met and the average cathode-Z is close to 50-ohms.
>
>Or the old Alpha trick of using an un-un transformer with parallel tuned
>networks (when adding a second 8877 in the 77DX) can be employed.
>This is much easier than trying to tweak a pi network for each band when
>converting a 50 ohm tuned input to >50 ohms out. Only one part needs
>to be installed. (the un-un) This will also work with an existing pi network
>tuned input assembly. Just wind an un-un for the desired step-up/down
>ratio and solder it in.
>
For me, changing the tuned inputs from 52-ohms out to 26-ohms out is 
preferable,  Decrease L1, increase Cout, make Xc-in=20 - 25 ohms (Q=2.5 - 
2.0).  Tweak for best match.  However, a second 8877 is only going to 
make c. a 2db difference at the Rx end, so it's a questionable 
expendature -- especially in view of extant tank problems when the second 
8877 is added. 

cheers, Phil.  

-  R. L. Measures, 805.386.3734, AG6K, www.vcnet.com/measures.  
end


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