ORIGINAL MESSAGE: (may be snipped)
On Mon, 21 Oct 2013 13:36:18 +0000, Manfred wrote:
>
>On the highest bands, the problem is another one: All that tube
>capacitance and stray capacitance forces us to use a Q higher than we
>would like! For example, on 10 meters with a 4000 ohm plate, a Q of 10
>would need a tuning capacitance of just 14pF. Good luck finding a tube,
>and a construction method, that keeps the tube and stray capacitance
>lower than this!
REPLY:
The solution to this problem has been known for decades. A simple coil
between tube anode and the rest of the circuit provides the equivalent of an
L-network which steps down the tube impedance to a value that is easily
handled. Details can be found in any recent ARRL handbook in the amplifier
section. The best part of this "trick" is the coil is most effective where
it is needed, i.e. the higher frequency bands, and effectively "disappears"
on the lower frequencies. Problem solved for about a penny's worth of
copper.
73, Bill W6WRT
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