[Elecraft] KPA100/KAT100 trouble

[Don Wilhelm]

Chris,

I am pleased to learn that you have had success with the diode 
replacement.  They are a bit difficult to reach, and there is no reason 
they cannot be placed on the bottom of the board as you have done.
Do correct the power supply situation before drawing any further 
conclusions about maximum power output, but you can calibrate the 
wattmeters even with your limited current battery.

You can calibrate the wattmeter in the KPA100 and the KAT100 at 10 watts 
and that typically provides good results over the entire range.  The 
KAT100 manual gives you voltage measurements to do that calibration and 
will normally yield quite acceptable calibration results - just follow 
the manual instructions.

Actually doing the KPA100 wattmeter calibration at 10 watts will provide 
good accuracy over the entire range too (there is scaling at high power 
built into the KPA100).  Power only the base K2 and the power control 
steps will provide more resolution during the calibration, and if you 
have an accurate dummy load, you can read the RF voltage across the 
dummy load with an RF Probe and calculate the actual power.

The K2 LED bargraph does not have sufficient resolution to measure the 
actual power output - if you have the Elecraft DL1, you can use it with 
the built-in detector to determine the actual power, but lacking that 
tool, use an RF Probe and a good 50 ohm non-reactive dummy load to 
calculate the power - most RF Probes will withstand RF voltages across a 
50 ohm load for up to about 18 watts.

73,
Don W3FPR

Christopher A. Kantarjiev wrote:
> Don,
>
> It's taken me several weeks to get to this, but tonight was the night. 
> I had tested and determined that the base K2 was fine, but neither the 
> KPA nor KAT controlled power correctly. The parts folks had sent me 
> diodes.
>
> Boy, what a nuisance these are to replace! Julius N2WN had suggested 
> putting the KPA's diodes on the underside of the board, where they are 
> easier to get at, and I followed that advice. For the KAT, there's 
> just no good way to get at the backside of the board w/o removing all 
> the connectors. I used a stainless dental pick to clean out the holes 
> from the front, and soldered from that side, too.
>
> Power control works great now. Both bridges seem to want to be 
> recalibrated - the max output is about 75W, even when I have 100+ 
> dialed in. I didn't do the original calibration on these, so I'm not 
> certain of how close they were ... and I guess I'm not sure that I 
> measured for full power out when I bought them.
>