[Elecraft] K3 and KX3 questions for Wayne

[Johnny Siu]

Hello Gentleman,
I met both Wayne and Eric in the past, they are thick skin and like questions right in front of their faces.  Some questions for them to address will give them more desire to do better.  In return, we are benefited.
Actually, I don't mind having a KXPA100 delivering 100W under 12V power supply.  Just leave Wayne free hands to Wayne to answer and I trust he is in a better position to do so.
73
Johnny VR2XMC

      寄件人︰ Kevin Stover <kevin.stover at mediacombb.net>
 收件人︰ elecraft at mailman.qth.net 
 傳送日期︰ 2016年05月23日 (週一) 8:20 AM
 主題︰ Re: [Elecraft] K3 and KX3 questions for Wayne
   
Further down in the same online spec page it states "Compact unit ideal 
for both desktop and mobile use". Note *mobile* use where the electrical 
system supplies more than 13.8V with the engine running.
I find no mention of the KXPA100 being developed as a "portable" amp. I 
have done searches of all Elecraft docs concerning the KXPA100 and find 
NO mention of the word *portable* anywhere. Nor do I find any mention of 
some nefarious board swap early in the products life.

Maybe the OP assumed because it has a carry strap that it is a portable 
amp. Well...My TS520 has a carry strap and a DC-DC converter. No way 
that can be classified as portable, it weighs 37lbs.

To be fair I have run it at field day but we had a 10KW diesel powered 
generator on a trailer. Power was NOT and issue.

On 5/22/2016 4:46 PM, Jim Brown wrote:
> Michael,
>
> A careful reading of the online data sheet for the KXPA100 is 
> instructive here.
>
> http://www.elecraft.com/KXPA100/kxpa100.htm
>
> The first line says "100 watts at 13.8 V, 1.8 to 29.7 MHz and 80 watts 
> 50-54 MHz PEP CW/SSB/DATA; ± 1 dB"
>
> Two points: First, the amplifier is rated for 13.8V, NOT 12V. Second, 
> the rating is +/1 dB, which is +/- 20% power. Thus, 80W on the HF 
> bands is within spec for 13.8V at the amplifier terminals.
>
> The second line says "13.8 VDC powered; 20 A typical current drain (11 
> V with lower output. 15 V max)"
>
> This clearly means that the unit is designed and rated for 13.8VDC, 
> can be operated from 11V to 15VDC, and will have reduced output at 
> lower supply voltages.
>
> Obviously, Ohm's Law dictates that resistance of the DC supply 
> conductors will reduce power supply voltage at the amplifier 
> terminals, so while we may have 12V or 13.8V at our battery terminals, 
> the voltage at the end of 6-12 ft of cable will be a bit lower with a 
> 20A load. For example, the drop in 6 ft of #10 is 0.24v; for #12, it's 
> 0.38V, and for #14, it's 0.6V.
>
> As others have noted, the operating voltage in so-called 12V DC power 
> systems using lead-acid batteries is not 12V, but rather 13.8V. If you 
> buy an AC power supply for ham gear, it will likely leave the factory 
> with its voltage regulator set for 13.8V. Open the manual or the spec 
> sheet for nearly all ham gear and you will find the supply voltage 
> specified as 13.8VDC.
>
> 73, Jim K9YC