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Re: [Amps] IM distortion and such

Subject: Re: [Amps] IM distortion and such
From: Joe Isabella <>
Reply-to: Joe Isabella <>
Date: Mon, 26 Jun 2006 08:10:35 -0700 (PDT)
List-post: <>
Normally I stay out of these, but in this case I have to say something...
We're not building bridges here where people can lose their lives if a design 
stretches tolerances a bit.  Granted, you could be out a few hundred bucks if 
you screw up a tube, but multiple deaths are not a result of overdriving a tube.
I don't care how good of an engineer you are, nobody has been able to build 
common sense into their designs.  Everybody wants the world in a box that 
auto-tunes, auto-adjusts drive, auto-shuts down if something is wrong, and 
auto-troubleshoots itself when it breaks.  Then they want a 3 kW version for 
$1,000.  Folks, you get what you pay for -- Alphas get close.  I happen to work 
on 500 and 1000W amps that nearly do everything I just mentioned made by Harris 
for the military.  No, they don't run the "illegal limit", but they're pretty 
robust.  Trust me, you don't want to buy one of those "NIB" from the 
I'm happy with my 3K-A.  Paid less than a grand for it, 2kW+ out, and tubes 
that cost $300 for two.  "What-a-baagin"!!  
Joe, N3JI

----- Original Message ----
From: Will Matney <>
Sent: Sunday, June 25, 2006 7:39:39 PM
Subject: Re: [Amps] IM distortion and such

It's according to what kind of audio amp. Guitar amps are designed to purposely 
introduce distortion. That's where the squeal of the electric guitar comes 
from. The bands actually prefer this. However, if one is an engineer, and you 
have a maximum rating curve, it is a liability to ever go outside the curve 
into the over load region. That's like saying I'll put my stamp on this bridge 
which I know is going to deflect more than allowable published tolerances, and 
that I think it can get by with the added stress, even though I am over the 
maximum curves for tensile and yield strength. Then an automobile drives over 
it and falls in the river. Who's liable? Whether electrical or mechanical 
engineering, an engineer should always look at this. Though running a tube out 
of spec probably wont kill anyone, the manufacturer better be ready to replace 
tubes or the entire amp if the customer is dissatisfied as a suit will sure 
follow if they don't. If ran in spec, one has nothing to
y about, and has published data to fall back on. This from an engineers point 
of view.



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

On 6/25/06 at 4:00 PM k7fm wrote:

>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 might be easier to grasp what Tom is saying if you think of audio 
>amplifiers.  Assume a tube manufacturer specifies a tube for audio 
>distortion.  However, the manufacturer of the audio amplifier is looking
>minimum distortion.  If he finds that running the tube outside of the
>specified by the tube manufacturer gives consistently lower distortion,
>it would be good engineering to do so.   In some cases, tubes might be
>selected for those parameters that met the goals of the engineer.  In some 
>cases, the plate dissipation might be exceeded to get closer to class A.
>Colin  K7FM

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