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On Wed, 4 Nov 2015 06:57:59 +1300, Steve wrote:
>
>If I understand correctly, the L match is just a normal pi network, but
>missing the input capacitor. I am not sure how that is tuned in
>operation, or if I'm on the right track at all there.
REPLY:
No, it's not a pi network, it really is just an "L" network, made up
of the tube's output capacitance (including a few pF of stray
capacitance) and a coil. That's all. It steps down the relatively high
plate impedance of the tube down to a lower value, somewhere around
500 ohms or so which is what the actual tank circuit "sees". At 500
ohms, the tune capacitor of the pi network is relatively large
compared to what it would be without the "L" network.
As I mentioned, this method is covered in any recent ARRL handbook in
the amplifiers section.
I will send you a separate email with some pictures of how I modified
a Heathkit SB-1000 for six meters and you can see how it looks. Using
this technique I was able to keep the original HF tune and load
capacitors and it works like a charm.
If anyone else wants the pictures, drop me an email.
73, Bill W6WRT
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