[Elecraft] K3: Do you "Juice" your K3?

[Jack Smith]

If you look at the DC current, you'll find  that lower supply voltage 
for modes such as RTTY and CW are considerably more efficient for the K3.

My measurements suggest that for a given output power, the K3 is more or 
less a constant current load. At 100 watts, the current is around 18A, 
so the difference in heat dissipation within the K3 between a supply 
voltage of, say 12.8V and 14.0V is 22 watts, all for the same RF output.

As I've said before there are  reasons on SSB mode not to run with low 
supply voltages, but on single tone modes, such as RTTY or CW the K3 
will have less heat dissipation with lower supply voltages than higher 
ones.

http://www.cliftonlaboratories.com/elecraft_k3_efficiency.htm has some 
of my efficiency measurements.

Jack


Ed Muns wrote:
>> During the NAQP RTTY, at one point I was calling a solid 
>> stream of CQ's at 100 watts output on RTTY and not getting 
>> any replies. I was watching the PA Temp, and it climbed up to 
>> 65C and looked like it wanted to keep rising pretty quickly. 
>> I think hi temp shutdown is at 84C. I backed off on my CQ's 
>> and used the other radio for a while. I had the fan speed 
>> locked on step 4. All of this was at 13.8VDC. With any kind 
>> of heavy duty usage, I don't think cranking up the voltage is 
>> a good idea. A better idea is to buy an AL-1500 or similar 
>> low drive amp, which will give you 1500 watts out with 50 
>> watts of drive. NOW, we are talking "juice." ;)
>>     
>
> This is interesting.  I run 100 watts output on RTTY, CQing and working
> stations at a continual flow, and the fans hardly run at all.  The PA
> temperature stays down.  I wonder if there is something unique going on with
> your K3(s)?  One user found a fan wire impeding the blades of one of his
> fans and even on CW, he had the same experience described above.
>
> Ed - W0YK
>
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