[Amps] Plate Impedance, ARRL

Jim Kearman jkearman at att.net
Wed Apr 26 12:56:41 EDT 2006


From: "Will Matney" <craxd1 at verizon.net>

> I'm not knocking using 1.8 as that's what I use and it works. The reason I 
> broought all this up is that they do not make it clear from what I read that 
> these factors are for triodes only that I seen. 

I suspect that when that section was written, the League was publishing only triode amplifiers. For many years until George Daughters published his 4CX1600B amplifier, all Handbook amps used triodes.

I got the insight into the differences from reading Rich Measures's site. It's interesting to read the history of his Handbook chapter, which was presumably rejected mainly for political reasons. As load impedance calculations are based on the plate-voltage swing, it seems intuitive that the k factors for triodes and tetrodes/pentodes would be different. 

> Also, the terms differences that 
> we use where they say the plate load resistance is the same as plate impedance.

Assuming the load is matched, the plate is looking into a non-reactive impedance, so the terms could be interchanged. Considering the load as an impedance, though, is more in line with the fact that we are dealing with ac and reactances, not dc and pure resistors. My guess is the confusion stems mostly from erratic editing of the Handbook. Certain chapters are chosen for revision and updating each year. Other chapters, even though they may contain known errors, are not touched. It might pay to take several years' worth of Handbooks, cut them up, and reassemble them to produce one relatively error-free copy! 

73,

Jim, KR1S
http://kr1s.kearman.com/


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