>> ** 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.
>
** True, Tom. but operating Q is designed in.
>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.
>
** Again true, but such was apparently not the case.
>Short two turns in the middle of a tank coil that lives happily, and watch
>it overheat around those turns.
>
** was such reported by Carl?
>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.
>
** No forced air cooling on the tank-L would cause heat buildup -
especially in RTTY mode.
- R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K,
www.vcnet.com/measures.
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