CO2 power supplies, regulated?

[phenol]

I have a CO2 laser power supply not unlike the large vairety of factory-made chinese co2 supplies intended for engraving machines.
Those of you who own one know that tube current can be adjusted with a simple potentiometer hooked to 3 of the typically 6 control terminals.

My question is if the output current is actually regulated or not.

I noticed that the cathode return wire is electrically grounded to the cabinet of the power supply i have. This leads me into thinking that there isnt any feedback loop controlling the output current. I also saw that the current changes as mains voltage fluctuates.

Sure i could use an external shunt resistor plus some sort of loop compensation and feed the error signal back to the power control port of the PSU, but i was thinking that those things were regulated...or is my own a dud?...

 

[Cyparagon]

How much does it vary?

 

[phenol]

How much does it vary?

I dont know how much, it depends on how much the input voltage sags. I just noticed that if i plug a heater in the same extension cord, output current droops and then recovers when i unplug it.

i asked the psu maker and they confirmed /as far as i could understand/ that it is not regulated. At least, it doesnt need ballasting to work.

I rigged a quick feedback loop wit an opamp and some shunt resistance from tube's cathode to ground. The output of the op amp goes directly to pin 5 of the green control connector on the power supply. It keeps tube current constant and independent of line fluctuations