Steve Nosko wrote:
"A (tube) amplifier is in conjugate match conditions. It is dissipating
10 watts in its plate. This is the limit of its plate
dissipation----There is also 10 watts in the load.

Now assuming you can, increase the (plate) supply voltage by , say
20%---(may be the fatal flaw)."

Likely so. If everything remains linear, 20% more voltage increases
power by 1.2 squared, or 1.44 times. If the tube was already dissipating
its maximum sustainable power, expect an early failure due to the
overload.

If you were not already in a maximum power transfer condition, and a
condition which might provoke flashover within the tube, a readjustment
of the match might shift more of the available power to the load and
thus relieve the tube of some of the dissipation.

Best regards, Richard Harrison, KB5WZI