ORIGINAL MESSAGE: (may be snipped)
On Wed, 30 Oct 2013 21:18:51 -0500, Jeff wrote:
>Bill,
>
>Did you use a tuned input on those two amps? The reason I asked is that I
>saw quite an interaction between the efficiency of my gi7b and the tuned
>input trimming that I was never really able to figure out.
>
>Also, what tank Q did you build the design around?
>
>I'm planning to build a GS35b amp for the higher bands this winter.
>
>73/jeff/ac0c
>www.ac0c.com
>alpha-charlie-zero-charlie
REPLY:
Yes, I always use a tuned input on my amps. Design Q for the output tank was
12 per the G4AXX spreadsheet.
You might be interested to know that in both amps, I replaced the GS35b with
an 8877, changed the cathode zener and filament transformer and immediately
got into the 60%+ efficiency range. The HV and input and output circuits
were the same. The only conclusion I can come to is the tube itself just
isn't as efficient as others.
As I said, if you can accept the 10% or so reduction in efficiency,
everything else about the tube is good. Especially the price.
When you build your amp, you can use a Coleman lantern replacement glass for
the chimney. It fits perfectly and can be fastened to the chassis with a few
dabs of silicon RTV, which is easily removed with a knife if you ever have
to. And of course, it needs no socket, just some careful metal work and some
simple home made clamps.
Have fun!
73, Bill W6WRT
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