The sound could also be a high voltage spark between a tube end and the case. You should check if you have enough distance from the tube to the case on all sides. Check if you mounted the new tube too close to the case on one side, or the new tube is longer than the old.
If the current meter is reading the correct value of current then the tube is likely being driven ok and the problems is not the supply.
It could be an arc outside (as @cprezzi ) mentioned or also inside the tube.
Does this happen only during a job or also intermittently if you hold the test button? Does the current bump up or drop lower?
Might be related:
I recently worked with someone on an unusual LPS problem where there was an internal arc and current leak from the outputs end epoxy seal through the water bucket to ground. He was blowing LPS every few months. Turned out he was using standard anti-feeze which is more conductive and a corona track had formed in the output seal. He replaced the anti-freeze with distilled water and from what I had heard fixed it? Very weird.
I have no way of confirming cause and effect in this weird case but I can verify that normal antifreeze is more conductive than RV antifreeze and is not recommended.
I don’t know if the corona leak was caused by a defect in the output seal or if the leak was caused by using standard antifreeze. I have also heard reports of folks feeling a tickle from their water bucket and wondered if the two were related. Is there current flow through our reservoirs in normal operation?
Don, that problem has been reported, I’ve noticed a product on EBay http://www.ebay.com/itm/322204363935?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT that might help - although I don’t know if it connects any differently to the HV on the tube. If your machine is in a spot where a direct to ground rod connection can be made - it’s a good idea.
Cloudio, now that you mention it my new tube is mighty close to my first mirror. I had my head down there looking at the end of the tube trying to identify an issue, but I was mainly focused on the bubble in the end at that time. I’ll take another look when I get back to the laser.
Don, that was my initial thought, but the sound is coming directly from the power supply. Much louder when I have my ears there vs the tube.
It does happen when I press the test button as well. Its funny…when the control knob is turned up passed half way, the sound will reflect on the meter with a small (almost unnoticeable) DROP in power. If its below half way it reads as a small JUMP in power.
Really strange.
I have checked with my hand in the water and haven’t noticed any current t in there yet
@Tim_barker pretty sure that if you are having an arc you will see it.
Turn out the lights and see if you can see and arc. If not;
Turn out the lights, setup and take a video of the tubes output end in operation. While operating with the rear cover open position yourself in front of the machine with safety glasses, start the video and push and hold the test button hopefully until the squeal starts.
In the video look carefully at the end of the tube and see if you can detect an arc inside the tube.
Hint I have used a selfie stick to take videos while out of the way of the laser compartment,.
Please be careful and wear glasses.
Will do, Don. I’ll get a video here as soon as I am back home to my laser.
@Tim_barker some thoughts;
If there is a HV arc it acts somewhat like a short and the supply might make the noise as the load changes, not the tube.
Potential explanation of the strange pot reaction;
If the supply is running nearer capacity (pot turned past 1/2) when the short happens the supply is saturated by the additional load and the current drops.
If the supply is running below capacity when the short happens the supply can provide more current and the meter jumps up.
I am guessing … HV power is a strange animal… and BTW dangerous!
That makes sense Don, watts is calculated as voltage times amperage so depending on which is closest tot he max available - one or the other has to change.