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Re: [Amps] IM distortion and such

To: Joe Isabella <>
Subject: Re: [Amps] IM distortion and such
From: R L Measures <>
Date: Mon, 26 Jun 2006 11:02:22 -0700
List-post: <>
Joe -- Since 3-500Zs do not have an indirectly-heated cathode, the  
only issue about overdriving them is non-linearity.

On Jun 26, 2006, at 8:10 AM, Joe Isabella wrote:

> 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 <>
> To:
> 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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