[Amps] IM distortion and such

[Will Matney]

Tom,

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. Where 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.

Best,

Will


*********** 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 
>bridges.
>
>73 Tom 
>
>
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