Potentiometer Replacement

K40/smoothie.

The stock pot that is installed on the k40 machines is a 1 turn 1k 2 watt pot. With this pot, my full operating range that I chose was 0 to 16ma. 16 ma was about a half turn on the pot at best. I bought a 1 k 10 turn pot the replace the stock one and installed it. It worked very well and now 5 turns of the pot was 0-16ma but I still was left with another 5 turns unusable so I added a 1k resistor between the +5v supply and the pot and it is now functioning perfectly as I intended. At a full 10 turns, I have a 16ma reading on my ammeter. Not only does this give me great resolution and accuracy for setting the tube current, it also makes it impossible to set my current higher than 16ma protecting my tube from my overzealous finger!!

I would recommend this simple modification to anyone running a k 40 with a pot.

4 Likes

That’s a clever idea for that particular modification!

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