Paul Ferguson wrote:
> I have a 10-year-old QRO HF-2000 amp. It has two Amperex 3-500Z
> tubes. You can see info on it at: http://www.qrotec.com/
>
> It used to output 1,000 watts or so on all bands. Now it outputs
> 1,000 watts up to 20 meters, but only about 500 watts on 17 meters
> thru 10 meters.
>
> On 20 meters and lower, grid current runs about 150 ma and plate
> current about 500 ma. Plate voltage is about 2,800. Input power runs
> 50 - 75 watts.
>
> On 17 meters and higher, grid current is about 100 - 150 ma and plate
> current is 250 - 300 ma. A small increase in input power gives a
> large increase in grid current and little additional output power.
> Input power is 30 - 40 watts.
This is a symptom of light loading. You don't say about the value of
the load capacitor. If it sits at minimum C, then I'd suggest looking
for a parallel load C that gets switched out on the high bands. Maybe
the switch somehow doesn't disconnect the extra C??
jeff, wa1hco
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