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?
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
>
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
R L MEASURES, AG6K. 805-386-3734
r@somis.org
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|