[Amps] HF-2000 amp problem?

[jeff millar]

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