My old tube went pthht, so I decided to upgrade it with an 800mm, which they falsely advertise as 50 watts. It’s not working correctly and the beam isn’t dark like the old one. It takes near 5ma before it begins to affect paper and 10 passes on material the original 700mm tube could do in one.
Sounds like you alignment is off. Redo all the alignment, and make sure your mirrors and lens are clean.
Installed new Si mirrors and aligned at the same time, I can’t even check the first mirror under 4ma, it’s terrible.
Does it depends on the power of the supply? Did you Need a bigger supply? I doesn‘t now it, I ask just for my personal interrest 
Possible that you do not have a good connection at the HV side of the tube. I would re wrap the wire on the post after cleaning it with a bit of fine sandpaper, and strip the wire back to a new clean section.
It’s a metal head with a screw.
Forgot to add, I did cut and strip it back a little, so the connections are solid. This power supply is supposed to handle this size tube, if anything, the flyback could possibly be weak, but my old tube worked better even when it needed replaced.
It does sound like it is a bad tube then. I would contact the distributor and request they send you a new tube. I personally only deal with Cloudray laser. They sell excellent quality tubes, and have great customer support 7 days a week.
I was considering putting the old tube back in, but had an accident with it that caused the glass to break at the cathode terminal/post.
I have CloudRay optics, but decided to go with this other place. Then I found out they were basically just a drop shipper and have to contact the actual supplier in China. Bleh.
These tubes do not start to ionize until about 4-5 ma and will not run properly that low. Try it with 10-20 ma.
Even at 20 it can’t compete with old Betsy.
Actually, I never ran old Betsy past 17mA.
Don, the 800mm doesn’t, or the 700mm as well? I was able to lightly engrave at 3mA with the 700mm.
It made a fizzing noise that low, but I actually liked the way it worked, the texture it gave on acrylic while fizzing. These were done around 3-4mA withe the old tube while still fizzing.
The inonization point is pretty uncertain at low current I wouldn’t be surprised if each tube is pretty different.
Another thing I discovered is that you should go for a tube with a pinkish-purpleish center because it’s some kind of gold catalyst to help with tube longevity.
I replaced a tube to discover that the old powers supply was actually the problem
Was it weak or not working at all?
@JamieR it was weak. Then replaced with new one and t was only marginally better until I replaced PS