Hello, does anyone know why I am not getting a clean marking on my laser when aligning?
I cleaned already the 3 mirrors.
Sadly, your tube has probably shifted into TEM01
See other posts tagged tem01 for more examples.
I read a few about that, so I can start to think that the tube is dead.
In the meantime I get a new one, can I still use it?
Yes you can still use your tube in a TEM01 mode, it’s just going to have a lower effective power output.
Ok, thanks
The quality of the engraving is compromised?
Do you know where I can buy a new one either in USA or Mexico?
From the K40 Intro at the top, you will find:
You’ll see several sources there. 
Do you recommend the Ten-high tube?
Do you recommend the Ten-high tube?
I’d go with the SPT if I had a K40. It’s generally considered a well-known and high-quality brand, and it costs less than the Ten-high.
I see that @NedMan opted for the SPT for his K40:
Yes, I highly recommend the SPT tubes. I’ve been very happy with mine.
That’s crazy. What does it look like on the first mirror?
That was the first mirror.
It’s crazy. I decided to give it a try and WOW… cuts way way better that the original one.
Less power and passes needed. Actually it cuts at one pass and less power.
The original one needed 4 passes and more power to cut
If that’s the shape of the beam coming out of the tube then there is a problem with the tube. Sould be a solid dot. Unless the beam is hitting something else before it gets to the first mirror. Can you give us a picture first mirror and tube end in the tube enclosure?
Reminds me to point something out: If you don’t yet have an analog ammeter, strongly suggest adding one. That’s what measures actual power flowing through the tube.