[AMPS] HF2500 grid current readings

[Rich Measures]

>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. 
>
Eric:   What is the heater voltage, as measured at the tube sockets?  I 
know that this is not an easy measurement to make, but it may provide a 
clue as to what's causing the phenomenon you described.  
>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 ??
>
yes.  The problem was determined to be heater voltage that was higher 
than Eimac's maximum rated heater voltage.  .  

>c: Am I worrying too much as the tubes are rated at 80ma MAx per pair ???
>
Eimac has no max. current rating for the grid of a 3cx800a7.
...snip...
Rich---

R. L. Measures, 805-386-3734, AG6K   


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