### Calculating Tank Q, Tune C (C1), and Optimal Anode Load
Resistance (R_{L})

Tank Q, the reactance of C1, and the optimal anode
load resistance for linear operation (R_{L}) are
inter-related. Tank Q is defined as the capacitive reactance of C1
(X_{C1}) at the frequency of operation, divided into
R_{L} ---i.e., Q = R_{L}/X_{C1}......and
X_{C1}= R_{L }/Q. Note: C1 includes the anode
(output) capacitance (Ca) of the amplifier tube. At 29MHz, Ca may be
a sizeable fraction of C1.

R_{L }=
E_{supply}/2*I_{An} where I_{An} is the
average anode current in amperes.

(Note: There is some variation
in the constant in the denominator of the R_{L} formula. For
tubes with minimal anode-cathode potential at peak anode-current,
like the 8877, a constant of 1.6 should give more accurate results.
However, for tetrodes like the 8171, which use a high screen
potential (reduces anode AC peak-V), a constant of 2 seems to be more
accurate.

Thus, for a tube operating from 2500v @ 1A, whose
anode capacitance (Ca) is 10pF:

R_{L} = 2500v/2*1A = 1250 ohms.

Calculating C1

For a Q of 12.5, X_{C1}=1250 ohms/12.5 =
100 ohms.

The needed tune capacitance, C1 =
1/(2*Pi*f*X_{C1}). For 14MHz, C1 =
1/(6.28*14*10^{6}Hz*100 ohms) = 113.7pF. However, since part
of C1 is comprised of Ca, the net tune C is 113.7pF -10pF = 103.7pF.
At 28MHz, the tune C would be roughly: 57pF -10pF = 47pF. At 280MHz,
10pF has about 100 ohms of X, so, for a Q of 12.5, Ca furnishes 100%
of C1, so no tune C can be used.