Continued use is risky from a safety standpoint and may kill your PSU adding another 100 bucks to the bill once it dies.
I wish I could think of something else it could be, but the only longshot I can think of is if the tube is arcing to the water tubing on BOTH ends of the tube. Bear in mind IF this is happening, your water is energized and a safety hazard. Seems unlikely it wouldn’t ground out, but I’ve seen some pretty wild things happen in high voltage systems. Please be careful.
That would give the power a path thru (around actually) the tube and still carry it thru the ma meter. It’s a simple loop circuit with the + power connected to the fully mirrored end of the tube (right from the front) and the ground comes off the emitting end and goes to the ma meter. The - side of the ma meter is connected to the leftmost wire connection on the PSU, which ties to earth and system ground.
One other ‘way out there’ but possible scenarios is if the ma meter is burned out (open), the high voltage may be arcing across the coil inside the meter and that WOULD produce the sound you mention, and show jumping as the arc quenches and re-establishes itself.
A quick check with an ohmeter will tell the tale here, if the resistance across the meter
s terminals is more than about 100ohms, it’s bad.
(Make sure the power is off, the laser is SAFE and locked out so it can’t be inadvertently powered on before working on it)
Sure would be nice if it’s a $5 meter instead of a tube. Tube prices seem to be falling, but unfortunately, so does quality. I’ve been hearing of a lot of people with bad out of the box tubes. Some well known places sell tubes at premium prices, but don’t honor warranties, telling customers the factory water pump on the k40 is inadequate. There’s about 2500 K40s out there that seem to be working fine for far longer than 2 weeks on the factory pump.
If you do have to buy a tube, get several positive reports on the seller 1st.
Scott