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Re: [Amps] IM distortion and such

To: Tom W8JI <>,,
Subject: Re: [Amps] IM distortion and such
From: Peter Chadwick <>
Date: Mon, 26 Jun 2006 10:56:56 +0200 (CEST)
List-post: <>
Tom said:
>I think you are really saying an engineer shouldn't ever 
design outside what is actually published on a spec sheet 
that only covers a limited number of situations under any 
condition, even if the component manufacturer, field 
history, or direct testing show otherwise.<
It gives a manufacturer the chance to weasel out of honouring the 
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. One example that I know off involved a 
design of a video amplifier using wirewound resistors as collector loads to 
provide inductance for peaking. The resistor manufacturer changed the gauge of 
wire, used fewer turns, the inductance was less, and the amplifier didn't work 
any more.
This is why it's a good idea where possible (and that's generally only if 
you're doing a military program or a very big commercial one) to have a 
procurement specification to buy against, rather than a manufacturers data 
sheet. Especially for semiconductors!
Years of experience in the semiconductor industry lead me to state that analog 
IC second sources rarely are. That has been known to happen with tubes, too. A 
classic example is the 6BA6, which, when second sourced from eastern Europe, 
can be the Russian version, where cathode and suppressor grid are internally 
Peter G3RZP
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