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On 6/25/06 at 2:32 AM Tom W8JI wrote:
>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.
I'm not refering to Eimac but the numerous other suppliers and manufacturers.
This since Eimac no longer manufactures the 3-500Z as far as I know. You send
one in for warranty to the ones I'm speaking of, and tell them it was operated
over the recommended current, I can guarantee you they will reject it voiding
the warranty. I used to buy large quantities from CECO and Richardson, and they
had to do this as too many were ruining tubes then asking for warranty. There's
several suppliers who will not give a warranty on RF power tubes or transistors
over this.
>
>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
>advice.
>
>Once the line starts to deviate, that gets it into the
>non-linear regions, or is the way I was taught to read
>them.>
>
>Unfortunately you were taught incorrectly.
I should have worded the above differently and was my mis-wording. It should
have said deviate from the curve, or be outside the curve. Are you saying
Eimacs curves are incorrect and one can operate the tubes outside the
recommended curves? This being any tube, not just the 3-500Z. I'm not asking
about any products by Ameritron or the 3-500Z question from Rich. This is about
all the published information and curves that Eimac has published.
>
>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
>cycle?
>
>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.
I understand this, but isn't the published curves there to show the maximum
operating areas?
>
>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've read it front to back.
>
>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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Best,
Will
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