ORIGINAL MESSAGE:
On Thu, 13 Dec 2012 02:49:03 -0800, Jim wrote:
>
>I am building a GS-35B amplifier. The efficiency drops off a lot
>between 80M and 10M. Although the gain is quite constant. Does any
>body have suggestions as to why this is or whether this is typical.
REPLY:
IMO, the GS-35b is simply not an efficient tube. I built two amps
using one and in both cases I had to run about 3000 watts DC input to
get 1500 watts RF out. In both cases I replaced the tube with an 8877
and the efficiency immediately went up. With the 8877, only 2500 watts
DC input gave the same 1500 watts out.
I'm guessing it has to do with the design of the grid. It would seem
that the grid does not have "tight" control over the electron flow,
and some current flows around the grid, so to speak. Obviously I'm not
a tube engineer so those are just my impressions.
I had a conversation with one European ham who reported the same
results.
If you can tolerate the inefficiency, it's not a bad tube. In all
other respects it seems to be fine. The price is certainly right, it
needs no socket and a replacement glass from a Coleman lantern makes a
perfect chimney.
73, Bill W6WRT
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