[Amps] What am I missing?

[Bob and Bettina Groh]

My initial reaction was skepticism but the indicated input network is exactly 
what is indicated in the Eimac data sheet for the 3-500Z. Good pdf copy of the 
3-500Z is on this web site:

http://www.radiowrench.com/sonic/

Go down about 2/3's of the way toward the bottom and click on the 3-500z.pdf label.

This site <http://home.c2i.net/clank/ham/pa/3-500z.html> has a web page version 
of the data sheet with a link, at the bottom of the page, to the example circuit 
with all the component data.

I would have also liked to have had the actual app notes made available. I'm 
going to email the author and ask for those. The EIMAC web site had a pdf copy 
of the 'Care and Feeding of RF Tubes' but nothing else that seemed pertinent. 
Lots of other good stuff in there.

Anyways it does look like the use of parallel tuned circuits is fine because the 
basic input real parallel impedance of a pair of 3-500Z's must be close to 50 
ohms. I guess the proof of the pudding is in the eating.

73
Bob, WA2CKY

Pete Smith wrote:
> 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?
> 
> 73, Pete N4ZR
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