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Re: [Amps] SELL: Ameritron AL1200 Contestor's Amplifier

To: "Tom W8JI" <>
Subject: Re: [Amps] SELL: Ameritron AL1200 Contestor's Amplifier
From: R L Measures <>
Date: Sat, 24 Jun 2006 19:38:58 -0700
List-post: <>
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
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R L MEASURES, AG6K. 805-386-3734

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