[Amps] IM distortion and such

[Keith Dutson]

IMO, comparing current flow through semi-conductors and tubes is not wise.
Solid state devices can avalanche while metal in a vacuum has no such
characteristic that I am aware of.  I think this is why manufacturers of the
former are reluctant to be lenient on warranty claims.

73, Keith NM5G

-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
Behalf Of Will Matney
Sent: Monday, June 26, 2006 9:52 AM
To: amps at contesting.com
Subject: Re: [Amps] IM distortion and such

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. 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.

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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