I have a Commander HF2500 amplifier that seems to be experiencing high grid
current readings. I am wondering if I have some flaky 3cx800's, the meter(s)
are out of calibration, or I am just worrying for nothing.
On 20m I apply approx. 35w drive CW. The plate current is 1050ma or so. THe
plate voltage is around 2000-2100v. The load control is around the 22-25
mark, and the tune is at the 52-55 mark. I get 1500w dead-key on the Bird 43.
I have used 2 slugs and 2 meters just to check the RF readings. All ofthe
above seem to be close to the quoted values in the manual, with the excepion
of the Grid Current. The factory test(s) sheet quotes the grid current at
approx. 35ma. However, my grid ma meter is showing approx. 80 ma when I
first key down and it slowly drops to approx. 60 ma or so after 15 -20
seconds.
Line voltage is a stable 238-240vAC and doesn't drop on keydown.
After tuneup, I switch to SSB. With my TS950 and the processor (which results
in a strong continuos 35wPEP drive), the grid current reading still peaks at
60ma or so.
However, with my Icom 738 also running 35w CW the reading (grid) is the same,
but on SSB the grid current is around the 35ma point. On the Bird I still
show 1500w when the meter is in PEP, but obviously in RMS mode the output is
nowhere near that on both input and output . Also, the Plate current is
somewhat lower.
My feeling is that the Kenwood is really driving the amp on SSB with a solid
35w PEP whereas the 738 is only occasionally peaking the 35w drive level,
thus the lower plate current also.
Therefore, my questions are,
a: Is the manual/factory measurement sheet quoting grid and plate readings in
CW or SSB-PEP ?
b: Are my experiences similar to those of other HF2500 owners ??
c: Am I worrying too much as the tubes are rated at 80ma MAx per pair ???
d: Could there be something wrong with the amp I am overlooking (all looks
well. I
even measured some of the components in the grid metering circuit.) ????
e: Could I have some odd 3cx800's causing the high grid current ?????
Otherwise, the amp works great and I am happy with it, although somewhat
concerned.
Your input and suggestions are greatly appreciated.
73 Eric
KA2YKC@aol.com
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