C-3 Modification

This modification started as a small notice on the Elecraft reflector, and I got interested in the modification, because I still had some problems that my KPA-100 was oscillating on 7 MHz. Looking at the description and the diagram, I came to the conclusion that it could not make things worse if I did this modification.

	I started out by opening the station and folding the PA over to the right:
	Removing the last connecting wires between the KPA-100 and the K2 leaves the KPA-100 in a state where one can work further.
	Once you have removed all the screws required so that you get down to heatsink, you can see where I have removed the paint from the heatsink to ensure that a good electrical connection was present. I removed the paint from the heatsink using a rotating brush on my electrical drill. A bit rough, but it works.
	Another unauthorized modification that I have made is that I have mounted a 100nF capacitor over the speaker connectors to ensure that no HF was loose on the speaker.

Before	After

Part one of the modification was to change R4 from 100K to 39K. This was done without too much trouble, if you have solderwick.

Before	After

Part two of the modification was to add a 1K resistor on top of RFC3. This requires a bit more patience, but is doable.

The only left to be done was to assemble the KPA-100 again and to ensure that all the screws were used in the correct places. One little note about tigthening the screws. You have to use a lot more power and torgue than you think. Only then can you be sure that the KPA-100 does not start oscillating when transmitting on 7 MHz.

I used about 2 hours for the entire modification, from the time where I turned off the K2 and until the point where I could turn on the K2 again.