> ** Overdriving could be a possibility only if the tube was capable of
> substantially more emission than was needed to produce normal RF output.
> For example, If a 3CX3000A7 were used in a 1500w amplifier, only about
> 1/4 of the available emission would be used. Thus, if such an amplifier
> was driven to the tube's emissive limit, there would be c. 4x the RF
> circulating current in the tank - so the I^2 x R heating loss in the tank
> L would be c. 16x as great as normal.
Circulating currents are a function of loaded or operating Q as well as VAR
power (or current or voltage if you like and impedances). Even relatively
small tubes can overheat big wires when operating Q is high.
Not only that, there are other issues such as closed-loop currents in the
tank from transformer action when a portion of a winding with high multual
coupling is shorted.
Short two turns in the middle of a tank coil that lives happily, and watch
it overheat around those turns.
Certainly it doesn't take any great ability to understand heat was
excessive, but there are many possible reasons why the coil deformed. Not
just one.
73 Tom
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