I'm not familiar with that particular amplifier, but low 10m
efficiency is a common problem with 8877 amplifiers. In one of my
homebrew amplifiers, I had low efficiency in the 40% range until,
following a suggestion from Bob Sutherland W6PO, I relocated the tuned
pi input circuit capacitor C2 from the input band switch directly to
the cathode pin on the tube. Incredibly, efficiency jumped up into the
60% range. I was dumbfounded.
73,
Jim w8zr
Sent from my iPhone
> On May 22, 2017, at 3:45 PM, Gerald Williamson via Amps <amps@contesting.com>
> wrote:
>
> Going back to the fundamentals: overall efficiency for class AB2 is
> approximately .65 times (Qu - Ql) divided by Qu. Qu is unloaded Q and Ql is
> loaded Q.
>
> at 10m the Qu is higher because inductor losses are higher. In addition,
> part of the inductance includes band switch leads and other leads between
> tank circuit components. These leads are typically smaller causing losses to
> increase. In addition, tune C has a minimum value that adds to the total C
> and that increases the loaded Q which further increases losses.
>
> Gerald K5GW
>
>
>
>
>
> In a message dated 5/22/2017 4:14:25 P.M. Central Daylight Time,
> jmiklos@windstream.net writes:
>
> Does anyone have any first hand experience with this amplifier? I’m
> particularly interested in the 10 meter performance (Eb, Ib, Pi, Po).
> Maximum
> power output at .9A of Ib is only 1200 watts with efficiency at 43%. The
> lower frequencies are more typical for an 8877, ie, 1500 watts out with
> efficiency around 64% and Ib at .75A. Any theories to explain the low
> efficiency on 10?
>
> 73’s
> Buzz
>
> Buzz Miklos WA4GPM
> 2043 Hawkcrest Drive E
> Saint Johns, FL 32259
> 570-974-7433
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