Recently i acquired a CO2 laser cutter/engraver.
The power supply is kicking out some 20-30kV to run the tube.
Machine is grounded, checked gnd prong on the mains plug against the casing of the machine. Checked the socket with one of them plug in indicators for ground as well.

Here's the question - how long do i have to wait for the psu to discharge in case i need to change a tube or psu ?
it involves disconnecting a fat red cable from the post on the glass tube. It does have a fat connector inline, but red wire...close
Experience dictates to keep well away before full discharge (10 year old ignorant me decided to wipe dust off a crt's back, while grandad was fixing the tv... yep...ouch...)

PSU in question is MYJG100W, if anyone interested. https://i.imgur.com/jLB61Dd.png

Any procedures to deal with this safely (aka not getting dead)? Never had to deal with anything this HV since crt's went the way of the dodo.

 

It is not possible to give an answer to your question without knowing the effective capacitance at the output of the psu and the open circuit capacitor discharge current.

Since I would imagine changing the tube or psu are not frequent operations – if you require touching some part of the high voltage circuit, momentarily connecting a high impedance resistor (say 100kΩ) between the relevant point and ground will discharge the voltage to a safe level.

 

I've worked on supplies on the order of 100 kV 0.1A and 15 kV @ 1.5 A amoung others which are quite lethal.

It takes about 5 time constants. R*C to be about 98% discharged. With high voltage capcitors, they can charge up with no power supply automagiclly. Resistors might arc over. They are not rated for kV operation.

I had a large grounded insulated stick of sorts with a metal hook that could hook around something to discharge this equipment.

If you don;t have to work on it immediately, then overnight wait and then a discharge with an appropriate insulator/metal gizmo with an appropriate dielectric strength. Wood contains moisture, so don;t use it. PVC about 1' long and then some sort of grounded tip.

The 15 kV supply that I worked on had a 200 W 1 meg ohm (value might be off) resistor as a bleeder. The voltage divider was a series of 625K power resistors. They were about 6" long. The schematic is available online, so i could lookup the values.

Without a probe, your not going to know. With all probing, attache the probe with the system off.

If I were making a bleeder, it would be a series of resistors encased in corona dope and protected paying attention to the dialectric contant of air and the resistor voltage rating and/or body length.

Keeping the supply loaded with a short or resistor is your best option.

I often worked alone which wasn't good. There is the "one hand in the pocket rule" when working on HV. Good shoes, etc.

High voltage anodes of picture tubes were scary for me at maybe 12+ years old. I'd been working on tube gear then.