>"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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