[Elecraft] KPA 500 Power Amp.

[Bob McGraw]

My major concern, based on my actual measurements, is that operating a 
power amp of this type and design at reduced to significantly reduced 
power nets very poor efficiency.  In fact, my KPA500 at certain power 
levels below 500 watts will actually have higher heat dissipation than 
if operated at rated power. With this known, we all understand that heat 
is one of the most detrimental factors regarding solid state circuits 
and components.   I find many instances where hams operate at lower 
power with the thinking "it will save my tubes or transistors, etc."  
Based on measurements, this thinking is far from accurate.   I refer it 
to "old ham lore".

As to operating on 60M, the US power limit is 100 watts ERP (Effective 
Radiated Power) with reference to a 1/2 wave dipole. Unless one actually 
knows the loss and gain of the antenna system, just operating at 150 to 
200 watts is a blind shot in the dark. Do you know the gain or loss of a 
specific antenna?  Loss in a feedline is relatively easy to determine.   
Gain or loss in the antenna is quite a challenging project.   Of course 
who is going to know?  That is not important.  But what is important, 
one must be thoughtful of others, those that do operate within legal 
power limits.   Just because you can, is no sign you should do so.    It 
just isn't the ham radio way.   The methodology is different for 30M 
where the PEP is 200 watts.   Add a 6 dB gain antenna and one has 800 
watts ERP.   60M is not like that.

Perhaps the regulations should be re-written such that legal limit power 
is 1500 watts ERP in place of 1500 watts PEP.  That certainly would put 
all folks on a level playing field.   After all, FM broadcast and TV 
stations power is sated in ERP values.  I go back to changes when AM 
power was defined as 1 Kw DC input to the final stage.  That was changed 
to a power of 1500 watts PEP. With AM that equates to a carrier of 375 
watts modulated 100% for 1500 watts PEP.

While electricity may be cheap, the abuse and failure of solid state 
devices operating at high temperature is not cheap.  Just something to 
think about.

73

Bob, K4TAX


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> Message: 1
> Date: Tue, 24 Dec 2024 21:17:55 +0000 (UTC)
> From: Wilber Bandemer <bandemerw at aol.com>
> To: "elecraft at mailman.qth.net" <elecraft at mailman.qth.net>
> Subject: [Elecraft] KPA 500 Power Amp.
> Message-ID: <1476882602.6827589.1735075075108 at mail.yahoo.com>
> Content-Type: text/plain; charset=UTF-8
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> KPA 500 will not transmits on 60 meters. Please tell me what is wrong and what should I do to fixed this problem?73Wilber AB5WW
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> ------------------------------
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> Message: 2
> Date: Tue, 24 Dec 2024 13:32:23 -0800
> From: jerry <jerry at tr2.com>
> To: Wilber Bandemer <bandemerw at aol.com>
> Cc: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] KPA 500 Power Amp.
> Message-ID: <b69f1bd595b09352c8ff823dfa70bca8 at tr2.com>
> Content-Type: text/plain; charset=US-ASCII; format=flowed
>
> Why use it on 60M?  Legal limit is 100W ERP on that band.
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>                   - Jerry, KF6VB
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