ORIGINAL MESSAGE:
On Sun, 11 Nov 2012 17:59:26 +0000, Manfred wrote:
> When you push a tube
>with rather high capacitance to a relatively high frequency, you can end
>up forced to use a Q of 20 or 25 or even higher, just to absorb that
>high tube capacitance!
REPLY:
This question comes up often but there is an easy solution. Placing a simple
coil between the tube anode and the input to the tank circuit can transform the
tube's output impedance down to a lower value which can be easily matched with a
relatively large tune capacitor. The coil forms a simple "L" network using the
tube's output capacitance at high frequencies. At lower frequencies, the "L"
essentially disappears. The best of both worlds.
I have used this technique several times. It works like a charm.
For a full explanation, see any recent ARRL handbook in the amplifiers section.
73, Bill W6WRT
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