[Amps] IM distortion and such

[Joe Isabella]

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 manufacturer...
 
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 <craxd1 at verizon.net>
To: amps at contesting.com
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
 worr
y about, and has published data to fall back on. This from an engineers point of view.

Best,

Will


*********** 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
>for 
>minimum distortion.  If he finds that running the tube outside of the
>curves 
>specified by the tube manufacturer gives consistently lower distortion,
>then 
>it would be good engineering to do so.   In some cases, tubes might be
>hand 
>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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