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Re: [Amps] GS-35b 10M+6M dual-band

Subject: Re: [Amps] GS-35b 10M+6M dual-band
From: Steve Wright <>
Date: Wed, 4 Nov 2015 06:57:59 +1300
List-post: <">>

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.


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..

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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