[AMPS] 4-1000A Project

[Phil Clements]

>
> The is no "design impedance" for a switched inductor sitting on
> your table, because the design impedance varies with loaded Q
> and frequency.

Another variable B&W cannot cover in their spec sheets on the 850
series coils is layout. At first, that .8uh looks low for the 10 meter coil.
Put a cap across it and resonate it on your bench to 28.5 mhz.
Then drop it into your RF deck and see what happens to the C required
to resonate it on 28.5 mhz.


> People really get far too carried away with Q, because efficiency
> changes very little with Q as long as tank losses are low. Factually
> the lower the loaded or operating Q becomes, the higher the
> efficiency becomes until Q is the square root of the impedance
> ratios plus a tiny bit. When loaded Q drops below that value,
> network phase shift is 90 degrees or less and the network no
> longer behaves like a Pi Network.

This is easily observed when one has the luxury of a roller inductor
in the tank circuit.  If you are looking for a big peak when the Q is set
to 12, you are in for a dissapointment. Makes more sense to tune for
"max. clean" on the 'scope.
>
> The tank voltage can be many times the dc anode voltage, if the
> tank is "unloaded" or "underloaded", depending on the conduction
> angle of the tube and the impedance presented to the anode. But
> in a properly tuned class AB PA the peak voltage in the tank is
> always a bit less than the dc anode voltage.

If tank components are selected for "worst case" scenarios, a lot of
future heart aches will be eliminated  when the operator screws up
in the heat of "battle."

(((73)))
Phil, K5PC





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