[AMPS] HF2500 grid current readings

Mon, 25 Aug 1997 09:40:06 +0000

> From:          KA2YKC@aol.com
> Date:          Mon, 25 Aug 97 02:29:39 +0000

> 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. 

You could have flakey tubes, or it could be something heating in the 
PA. Does it behave exactly the same way on all bands? If so, it is 
likely the tubes. If it behaves differently, or acts fine on some 
bands it is in the tank system. 

> 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.

If you show 35 mA grid on SSB, you are probably splattering. Unless 
the Commander has a peak reading grid meter. 

35 mA peak **RMS** current on SSB is a sign of light loading.

> 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

The Bird always reads the same form of power. In peak mode you read 
the PEAK effective sinewave power value, and in AVERAGE mode you read 
the average effective sinewave power value.  

I know it's confusing, but in each case you are reading the RMS 
power. It's just that in one case you read the time averaged value 
and in the other the instantaneous peak value. Ny Viking even got 
that wrong in a wattmeter they sold once, hi.  

> a: Is the manual/factory measurement sheet quoting grid and plate readings in
> CW or SSB-PEP ?

Ask them! They know more about their particular amp than most of us.

> b: Are my experiences similar to those of other HF2500 owners ??

Same as an AL-800H, which uses the same tubes.  

> c: Am I worrying too much as the tubes are rated at 80ma MAx per pair ???

I'd worry a lot about the current drift, unless it's due to tank 
heating. If it is in the tubes, I'd get new ones right away.

> e: Could I have some odd 3cx800's causing the high grid current ?????

Yes. They could have internal problems. Or it could be the tank 
heating up. Why not ask Pat Stein? 

73, Tom W8JI

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