[Amps] tube impedance, figuring tank circuit values

[Jim Kearman]

From: "Gary Patterson" <gpatterson53 at hotmail.com>
> ok.... one guy says use the "open circuit voltage" the other guy say use the 
> loaded "operating voltage" ..................who is correct

Assuming you're making an adjustable matching network, you should be able to match a range of tube impedances while maintaining network Q within 12-15. Use your program to do some preliminary runs and pick inductance values for each band (assuming a pi-L) that fall within range. Then run the program again, specifying those inductances, but changing the Q and load impedance. This will give you the required ranges of tuning and loading capacitances. For example, for a pair of 4CX800As in the works here, I got these numbers for 160 meters:

160 meters, L = ~13.6 uH

Z=1460
Ct  = 595
Cl = 2760
Qo = 12

Z=1820
Ct = 602
Cl = 3236
Qo = 15

Ct is the plate-tuning cap, Cl is the loading cap (pi network, one inductor). I got similar results for 80 and 40 (it's a triband amp). By making the loading cap large enough I can cover the range of load impedances (depending on whose formula you use) with the same tuning cap and inductance.

73,

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