Step 7.
Due to the 2.88:1 mismatch at the load, neglecting network losses and
the small change in plate current resulting from the mismatch,
approximately the same mismatch appears between RLP and ZL at the
input of the pi-network. Consequently, the change in load impedance
changed the network input resistance RL from 1400 ohms to complex ZL ˜
800 – j1000 ohms, measured with the Vector Impedance Meter using the
method described in Step 2. To verify the impedance measurement of ZL
the phase delay of the network was measured using an HP-8405 Vector
Voltmeter and found to be 127°. Using this value of phase delay the
input impedance ZL was calculated using two different methods; one
yielding 792 – j1003 ohms, the other yielding 794.6 – j961.3 ohms,
thus verifying the accuracy of the measurement. However, because grid
voltage EC, grid drive Eg, and plate voltage EB are left unchanged,
resistance RLP at the plate has remained at approximately 1400 ohms,
leaving a mismatch between RLP and ZL at the input of the pi-network.
As stated above, this value of ZL yields the substantially the same
mismatch to plate resistance RLP as that between the output impedance
of the pi-network and the 17.98 + j8.77-ohm load, i.e., 2.88:1. This
mismatch at the network input results in less power delivered into the
network, and thus to the load, a decrease in the area of the RF window
at the network input, and a change in the slope of the loadline. (It
must be remembered that the input and output mismatches contribute
only to mismatch loss, which does not result in power delivered and
then lost somewhere in dissipation. As we will see in Step 8, the
mismatch at the input of the pi-network results only in a reduced
delivery of source power proportional to the degree of mismatch.)

Points in response:
1.We enter into a key remark in the first sentence: neglecting
network losses and the small change in plate current resulting from
the mismatch. By this statement the subordinate thesis being offered:
output source resistance of the RF power amplifier is non-dissipative
is wholly invalidated. The observation that the plate current changes
(and presumably plate voltage has not, unconfirmed in the protocol)
through the agency of mismatch must necessarily admit that the plate
resistance has also changed if only because it has been explicitly
admitted to through the dismissed current change.
2.To whatever degree (as dictated by the phase of the mismatch), plate
dissipation must also change. This is the common experience of
literally thousands of Amateur radio operators and has been commented
upon and reported for generations when through the unfortunate aspect
of phase, it becomes a destructive dissipation. Such reports often
attain dramatic legendary status, if only for the afflicted amplifier
owner (who may enjoy comedic celebrity among his peers).
3.Moving on to subsequent sentences, the reported values of complex
load resistance (792 – j1003 Ohms) seen from the plate looking through
tuning towards the new, mismatched load confirms that the plate
resistance must be impacted. If, as reported, the plate resistance
remains at 1400 Ohms, then there is a mismatch which is admitted to in
the text of the original. The final argument is based upon mismatch
loss, which from the perspective of the load, is that amount of power
not seen, but not lost by dissipation. That much is true from the
perspective of the load. The same would be true if we replaced the
plate tuning with a large resistor which would also reduce power to
the load, so such an appeal has nothing to do with the argument of the
subordinate thesis: output source resistance of the RF power amplifier
is non-dissipative. The nature of this particular plate mismatch
affirms the current indication, and rejects the conclusion of
non-dissipation (which is characteristically, and artificially
constrained to being exothermic when through phasing it could as
easily be endothermic).
4.A more careful protocol would allow for phase by lengthening the
13.5° length of coax to 103.5° (or more but well less than 180°) and
carefully noting the new plate current. In fact, other lengths should
be used to draw a more rigorous correlation.

73's
Richard Clark, KB7QHC