[Elecraft] K3 and KX3 questions for Wayne

[Kevin Stover]

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
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-- 
R. Kevin Stover
AC0H
ARRL
FISTS #11993
SKCC #215
NAQCC #3441



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