[Amps] Tuned Input - IMD and efficiency

[Tom W8JI]

> Ok, here we have finally gotten a documented number; 4 to 
> 6 dB HIGHER
> with an untuned cathode driven amp than a tuned input. 6 
> dB is a
> significant amount in my book.

I wouldn't take that number to the bank since the result 
would have to depend heavily on the impedance seen at the 
cathode, how the exciter behaves, and even cable lengths.

> Now it would be nice to see validation of these numbers on 
> real amps
> that we find in use today.

It might be something that never happens because there are 
too many variables.

> It is also very interesting reading in the last paragraph 
> regarding the
> coax used to connect the exciter to the amp.

If it affects efficiency, and I know it does without a tuned 
input or with an incorrect type of tuned input, it would 
also have some effect on IM.

Quite frankly I've never measured the IM change because not 
having a tuned input causes too many other headaches.

I highly doubt a simple shunt capacitor can be effective 
from 1.8 to 30MHz.

73 Tom