I have an odd problem with an Alpha 89 -only below around 1815 kHz on 160m,
nowhere else, and I am looking for ideas. The Alpha 89 tuning chart shows
that the loading control around 1825 is probably going to be near 10 on the
dial scale, and that is where mine wanted to be at 1.5 KW out about three
years ago. Gradually the setting has drifted down to 0, and the tuning
notch at 1.5kw has moved two bars above the center notch, I thought because
I was a max cap on the loading cap and need more cap.
The 89 and similar amps such as the 86 click in one additional padder on
160m. If this padder is paralleled, say with 150pf, I get back in range
with the loading control, but the tuning notch is still several bars above
center. Plate current, plate voltage, and grid current look normal.
Circuitwise I do not know how the tuning indicator works in the 89.
According to the scanty Alpha info, this is an unconventional circuit which
give a center indication when the tube is running at maximum efficiency.
Perhaps these are two separate problems or perhaps they are linked.
Can anyone give me an idea of what may be wrong? Can anyone explain how the
"tune for max efficiency" indicator circuit works?
73
Bob W2WG
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