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

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Subject: Re: [Amps] SELL: Ameritron AL1200 Contestor's Amplifier
From: "Tom W8JI" <>
Date: Sun, 25 Jun 2006 02:32:53 -0400
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Running a tube at other than the specified tolerances shown 
on the published curves by the manufacturer can and will 
void warranties.>

Eimac is long QRT on 3-500Z tubes, but they had a rating 
system called IVS duty. Contrary to what Rich implies 
everything Ameritron sold was run past the people 
responsible for the tubes. Eimac had no problem at all with 
the manual telling people they could TUNE to 550mA, and then 
back drive off until 400mA is reached. They never once 
rejected a tube for any sort of operational failure due to 
operating instructions or equipment design.

The only person I'm aware of who has a lifelong problem with 
the manual suggesting momentairily exceeding 400mA while 
tuning was Rich. As far as I know he doesn't work for Eimac 
and they didn't call on him for technical or warranty 

Once the line starts to deviate, that gets it into the 
non-linear regions, or is the way I was taught to read 

Unfortunately you were taught incorrectly.

It is impossible to look at one constant current line and 
predict transfer characteristics or odd-order IM distortion 
levels. If the constant current characteristic curves at one 
current value set the distortion level why would negative 
feedback reduce distortion? How could the output be linear 
when the tube is cut off for more than 140 degrees of the RF 

It is a transfer function problem. The level of IM 
distortion products is a function of the slope and shape of 
the gain change as drive level is varied.

If your read Care and Feeding of Power Grid Tubes (published 
by Eimac) all of this information is there. They even say 
they intentionally design to create an even-order curvature 
slope to avoid creating odd-order IM!

I suggest you look at page 96 section 4.3.2 of Care and 
Feeding. It's all there in black and white and worth 
reading. It will help sort unfounded opinions from the true 
facts. The ideal transfer characteristics for power 
amplifier conduction angles less than 360 degrees and more 
than 180 degrees (class AB) aren't even a straight line!

73 Tom 

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