[AMPS] Plate load charts

[Rich Measures]

>"Have you ever noticed"  (Now I sound like Andy Rooney)  how different the 
>plate load impedance/component value charts (C1, C2 L1 L2) for a given 
>plate load  change markedly between different publications ?
>
>I have noticed in the 23 edition of the "Radio Handbook" the chart for the 
>Pi-L network has values for the Q of 10. In the 1998 "ARRL Handbook" the 
>chart for the same plate load impedance has about the same values (within 
>5 % ) and that chart is for a Q of 12.  I have also noticed that different 
>publications give the formula for calculating the palate load impedance 
>different as well. Some books give a "K" value of 1.8 (23rd radio 
>handbook), and the some give the "K" value of 1.57 ???
>
>In the information sheet that I have from Eimac on the 3CX800A7,  this 
>sheet says that the plate load impedance value for the tube operating at 
>2200 VDC and a plate current of .5 amp is 2700 Ohms. This makes the "K" 
>value 1.56. 
>
>All of the values for "K" are for the tube operating in class AB2......
>
RL depends somewhat on the conduction angle which is a function of ZSAC 
(zero signal anode current).  Less ZSAC results in a lower conduction 
angle, and less K.  More ZSAC makes for a higher conduction angle and 
more K.  In any event, the exact value of K is not very important.  The 
idea is to put the Q in the ballpark and basically tune for max. out with 
max. drive.  

>On another note, I also have observed that the overall efficiency and low 
>quantities of heat, and the reliability of the tank components of H.F. 
>amplifiers that have a relative low value of plate load impedance 
>(1500-2000 Ohms) seem to be more efficient and run much cooler than the 
>high plate load ( 3500-4000 Ohms) amplifiers. 
>
I see no reason why.  Loss is mostly I^2 x R.  Circulating current is 
approx. Q x  anode-current.  With a low RL, there will be more 
circulating current. 
>..........
-  later, Jim


Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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