Replacing Power Pot

So a couple of years ago now (time files) I “upgraded” from the digital control on my K40 to analog control with amp meter and power pot. The power pot is a multi turn 5K ohm variable resistor recommend by @donkjr .

I use my k40 quite a bit and I’ve recently noticed that the voltage I measure across the pot, to determine a power setting, was bouncing around a lot when I turned the knob for the pot. Hooked up my meter and the pot was very noisy with the resistance bouncing around quite a bit. So it was obviously time to replace the pot.

Could not find a listing for a single pot like I originally bought so I bought this 2 pkg that came with knobs and now have a back up.

Easy fix with unsoldering and re-soldering some wires.

Much better.


I bought one of those from Aliexpress and it’s labeled as Bourne/Made in Mexico. Bourne were always the ‘goto’ potentiometer maker during my early electronics days.
I like the voltmeter addition, might have to try that.


My old one was a Bourns and the new ones I bought are labeled as AIPUGE.

Yeah the voltmeter is great as it allows me to dial to a voltage that I know will give me a certain tube mA. Another great upgrade idea from @donkjr .

1 Like

The voltmeter could be an add on for the new control panel design OR…

They will be a micro running a small touch screen as part of the control panel update,( looking after temperature , interlocks etc,) Perhaps I could have the micro monitor the voltage and display it as a mA reading
(no Geoff, finish re-building the damn laser first!)


The challenge with displaying a MA value relative to the 0-5V control voltage is that the V vs I curve changes as the tube wears.

I have thought about automating the laser current setup. The user enters the current needed and the controller runs a calibration program to find and set the right control voltage.

I decided this might overcomplicate the setup…decrease reliability and add to much cost …:slight_smile:

(no Don, finish re-building the damn laser first!)

You would need a:

  • D/A [05V]
  • 0-30ma current sense
  • Controller, keypad and display [or BT connection to phone app]

I’m definietly looking to solve problems that don’t exist :upside_down_face:

I think I’ll leave the contol panel as I’d planned. The microcontroller can just monitor temperature, interlocks, etc. The less I mess about, the better!