ORIGINAL MESSAGE:
On Sat, 11 Dec 2010 19:26:16 +0100, "Ulf (SM0NOR)" <ulf@sm0nor.com>
wrote:
>This makes me think of a third solution mentioned in the handbooks
REPLY:
There is a fourth solution that is easier than all the others put
together. It is disappears in depth in any of the ARRL Handbooks of
recent years. I have used it myself on a six meter amp and it works like
a charm.
You create a simple L-network in the plate circuit by adding a small
coil, typically about .5 uH or so directly from the tube's plate
connector to the rest of the circuit. The coil together with the tube's
internal plate to grid capacitance creates an L-network that steps the
tubes native plate impedance down to a value which the otherwise large
tune cap can handle with reasonable Q.
It sounds like black magic but it works. Get an ARRL handbook if you
don't already have one and look it over. It's in the chapter on
amplifier design. The best part of the design is its effect disappears
as you go lower in frequency and it has almost no effect on the lower
bands.
The best of all worlds.
73, Bill W6WRT
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