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Re: [Amps] IM distortion and such

Subject: Re: [Amps] IM distortion and such
From: "Will Matney" <>
Date: Mon, 26 Jun 2006 10:51:30 -0400
List-post: <>

No, your mis-quoting what I said. I said after I corrected and apologized, that 
deviating outside the curve (line was wrong), would be past it's maximum (IE 
higher currents, non-linear regions, etc.). I never once said IMD. I also never 
said you ran it continuously at 550 mA, as you did back it off. This I'm not 
even speaking of. To me what your saying is it's ok to run one temporarily 
overloaded. It may be ok, but from a warranty view they can refuse it, and have 
in several circumstances. Take a look at RF Parts page on sweep tubes and I 
think on a few others, there is no warranty over this. Didn't Ameritron make 
one using four 6LQ6/6JE6C's like a few others did? You can't lay this all on 
CBr's as Hams did it too. Radio Shack finally refused their guarantee on sweep 
tubes used in an amplifier. No more free replacements.

Here's a common scenario using the 2N3055 power transistor. Using its "Active 
region safe operating area" curve (Motorola), or really some straight lines 
making a curve, the 2N3055 says it's capable of around 8 amperes at about 14 
Vdc. However, most manufacturers of power supplies engineers rate them at 5 
amperes each, which is below the curve in the safe area. Lets say a power 
supply uses four of them, and the supply could carry 32 amperes while still 
being in the safe area, but the engineers say it will carry a 20 amp load. Now 
what if a designer said they'd carry a 40 amp load at 10 amperes a piece? How 
long would they last at this output? Would Motorola warranty them at this? What 
kind of reputation would the manufacturer get over their power supplies blowing 
pass transistors under full load? Are they willing to replace the product? Are 
they ready for a law suit from a disgruntled customer? The design falls back on 
the engineer, his license, and liability at worse case. W
 here I worked in mining machinery, it occurred often. Building one for ones 
self is totally different as the liability falls back on that person. Sure, 
here you can try things outside the curve, but a good engineer won't design 
something that may fail, or cause something to eventually fail for the public. 
That's just me and my opinion of the way I do it.



*********** REPLY SEPARATOR  ***********

On 6/26/06 at 6:03 AM Tom W8JI wrote:

>> It gives a manufacturer the chance to weasel out of 
>> honouring the warranty.........
>Not when they approve the operating conditions.
>> There is another reason, however, and that is that a 
>> manufacturer can have a subtle (or sometimes not so 
>> subtle!) change in manufacturing technique that produces a 
>> major performance change.
>I think the problem here is this thread, like many on this 
>reflector, has had a major performance change.
>The original subject was the manual of the AL80 says to load 
>to 550mA and then as a final step back off drive to obtain 
>400mA. This ensures the loading is heavy enough and grid 
>current is proper to handle ALC overshoots common with 
>exciters. That horrified a couple people, although 
>technically it is significantly better for all the 
>components in the tank circuit to do that, better for IM3 
>and IM5 performance, and it doesn't hurt the tube the 
>tiniest amount to do that.
>The second issue was someone claimed a curve in a constant 
>current curve at one plate current value caused distortion. 
>That statement is clearly in conflict with the actual cause 
>of IM. Eimac's design handbook actually repeats what I 
>posted, as would any reliable source. The final authority is 
>the manufacturer and real world results, not subjective 
>personal opinions or comparisons to cars falling from 
>73 Tom 
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