See below;
*********** REPLY SEPARATOR ***********
On 6/24/06 at 7:38 PM R L Measures wrote:
>On Jun 24, 2006, at 5:05 PM, Tom W8JI wrote:
>
>>> Rich writes:
>>>
>>>> P = I x E comes pretty close.
>>
>> Joe writes:
>>> That's fine but as I said: "I don't have the constant
>>> current curves"
>>> which means I do not have any way to determine the peak
>>> (or even
>>> average through the full RF cycle) cathode to grid voltage
>>> in the
>>> 3CX1200A7.
>>
>> At 2000w out with 120W of drive and 250mA of indicated Ig,
>> grid dissipation is only about 30W with a peak emission
>> current at the crest of the cycle of about 4 amps.
>> Contrary to authoritative guesses, the tube is well out of
>> emission saturation
>
>Tom -- So why do Eimac's published constant current curves on the
>tube begin to deviate from a straight line when the anode current
>exceeds 2.5a peak? Are you sure there's a 4A curve on the published
>graph? If there is, how about publishing a jpg of it on your Web site?
>
Running a tube at other than the specified tolerances shown on the published
curves by the manufacturer can and will void warranties. Once the line starts
to deviate, that gets it into the non-linear regions, or is the way I was
taught to read them.
>Tom -- As I recall, about 6-years ago you told us you had a letter
>from Eimac stating that the 3-500Z was linear at up to 550ma of avg
>anode current, even though their max rating is 400mA. When are you
>going to deliver?
>
>> and remains much cleaner than any modern
>> exciter we can buy (with the exception of a class A operated
>> FT1000 MK V).
>>
>> At 1700W and 200 mA Ig, grid dissipation is about 20 watts.
>
>My guess is that it's close to 70v x 0.2a = 14w.
>>
>> That's all at 3300V, things get much better at higher anode
>> voltage.
>>
>> Keep the grid below 300mA and you are OK, although I'm sure
>> even going well over 50W won't actually hurt that grid.
>
>Good point. Molybdenum melts at 2617ºC. .
>
>> The
>> limit they set on this tube isn't due to grid failure, it is
>> where secondary emission sets in.
>>
>> 73 Tom
>>
>>
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>>
>
>R L MEASURES, AG6K. 805-386-3734
>r@somis.org
>
>
>
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Best,
Will
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