Bill,
Thanks for your tips! I did seem to me that 10M would just be a few
more turns on the tank, and it seems now that 12/15 is just a few more
turns! I doubt I'd try for 40M as well - it's just not that sort of amp.
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.
It seems the task will be to build a 6M amp, and see how many bands I
can add without wrecking 6M operation.
Steve
On 04/11/15 06:00, Bill W6WRT wrote:
GS35b dual-band 10/6M amp? Any comments? Google can't find me a good
example of one of these, which is surprising..
REPLY:
That's a pretty simple amplifier. You don't really need a specific
schematic, just follow good design principles. The ARRL handbook is
your friend.
Just three comments:
1. Use the "L" matching design to compensate for the output
capacitance of the tube, which is too high for a "normal" pi network
out tank circuit, especially on six meters. Details are in any recent
ARRL handbook in the amplifiers section.
2. For best efficiency, use a plate voltage of about 4 kV. Running it
at about 3 kV will cost you about 10% in plate efficiency. 4 kV is
more than the specs allow for but it works fine anyway.
3. A replacement Coleman lantern glass makes a great chimney because
of its modest cost and high heat resistance. Hold it in place with a
couple of dabs of silicon RTV and put a few temporary spacers between
the glass and the anode fins to position it while the RTV dries. If
you even need to remove it the RTV is easily cut with a knife. Measure
the diameter carefully to be sure you get the right one, since Coleman
makes several different models. The right one will have a gap of about
1/8 inch between the glass and the fins, which is perfect.
Sounds like a great project. Have fun.
73, Bill W6WRT
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