K40 replacement tube

Hi all

K40 Tube froze and broke, live and learn i guess.

So i have a few querys. It looks easy enough to replace and i can see prices from around £50 + Postage on AliExpress.

What is the highest wattage tube i can use without changing the LPS?
Is it worth getting any particular brand of replacement ?
Should i buy from a UK supplier to emsure better quality/support ?

I dont use the laser heavily and i am experimenting with various materials at the moment so have nothing specific in mind ( Ply and Acrylic so far).

I have a 1500x1500 “Ultimate Bee” CNC from BulkMan3D and was also looking at Gantry mounting if anyone has advice (For/Against) or links to similar projects ?

thanks

The Getting Started with CO2 Lasers category has some posts that might help, especially Where can I find K40 replacement parts?

In general, CO2 power is a function of tube length, and to increase power you may need an extension to hold the tube, depending on the original tube power.

There are brands that are better than others. Reci and SPT ara generally considered high quality. You can search here for people’s experiences with them.

the stock tube in the K40 is more like a 30W or 35W tube which is one of the reasons why you need to have a current meter(mA) on it and limit the current to make the tube last longer. But when it’s replaced with a new 40W tube the LPS can still handle the output and you can drive it at full power because good tubes are tested for continued operation at full power. So it’s worth it to get a good grade tube.

Sorry for the delay. Thanks for the info you’ve given.

How delicate an operation to refit the tubing to the tube. It seems that both of the necks were where they broke so i am thinking they must be delicate to start with ?
Any existing posts on the recommended process please ?

thanks

The glass is pretty thick but no match for freezing water which literally can crubble mountains. Fitting flexible silicone tubing to them is not difficult be I would not use a hammer. I don’t know of any specific instructions but it’s generally, remove old tube, install new tube( replace calms if installing tube of different diameter), align mirrors.

Install new tube with water ports facing up, so that coolant fills the tube with no trapped air bubbles.

Is it advisable to use some sort of lubricant to help them go over the connectors more easily?

The glass is not that fragile but take care not to apply side torque to the stem.
I have never had trouble with pushing silicone tubing onto the water stems.

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Others have use fish tank heaters and other means to keep the cooling water in CO2 laser tubes from freezing and breaking the glass.

I bought direct from Vevor.

Hi Again

Finally received a replacement but it is showing similar results as before.

The ammeter shows 3-4mA at almost all % settings (initally tested at 99.9% on Digital) but goes UP to 5mA when on lower settings ( around 14-18% on Digital). I put the old Nano board back in when i was testing the old tube and noticed it never went above 3-4mA on that either ( i did not notice if it went up on lower settings).
Isnt the mA meant to be higher at greater %ages ? Can any suggest a surefire test or way to check that the right output is being received by the +ive on the tube?
Only changes are ammeter fitted ( worked fine immediately after) and rewired the new tube in. Seems odd that the behaviour is almost identical between the two tubes ?
If i need to start a new post for this let me know, bt thought it may prove useful to see previous info.

thanks

I thought you were replacing the tube because it had a freeze break.

Was it not working before the freeze?

By old tube do you mean the one that had the freeze break?
The Nano does not control the available power from the LPS, only the panel does that.

Yes as you increase the digital % the tube’s current should go up.
Do not go near the +(anode)… its output is lethal.
The only way to tell if the LPS is working is to check its controls.


Let’s start here:
Provide this info:

  • Control panel photo
  • LPS photo showing the input connectors and wiring.
  • LPS Model # if you can see it on the supply.

When you push the test button down on the LPS;’

  1. Does it fire?
  2. What current does it fire at?

Hi

Sorry would have been sooner but had to edit to get size down.
To Clarify,
Tube has been replaced once and this is a warranty replacement for that as it was deemed faulty. Everything you see below is the the warranty tube.
Everything is stock exept the ammeter. I could not see the LPS model sorry.



The laser fires ok, i have added the video below so you can see the issue.

thanks

Do you have a DVM and are comfortable using it?

Set the power level on the control panel to 100%

Down on the LPS there is a 3-pin white connector.
Measure the voltage on the pin labeled “IN” relative to ground.
Report the voltage on that pin.

Hi

I am getting 4.96v, taking grd from 1st Pin on the same connector. If you need it from somewhere else just let me know.

thanks

At that voltage on IN the laser should fire at near full power.

Just to be thorough.
Verify the cathode of the tube is at ground. I see the blue wire on the left connector of the LPS.

If you push the test button down on the LPS does the meter still show a low current?

What is the history of the LPS.?
How old?
How much use?

Fairly sure it is at ground as laser works but poorly. I have checked and tightened the Ammeter lugs to make sure. The only thing that i notice with the ammeter is a - marking on one lug, this is currently connected to the wire that goes back to the LPS.

Pressing the test button on the LPS shows the same around 4mA.

The K40 was bought as new ( customer returns) but was working fine pre break. I was cutting through 3mm clear perspex with ease( cant recall the setting, but it was 60% or lower.)
It has had barely any use at all, maybe 2-3 hours max i would say. I was just getting a feel for it when the tube got damaged. The ammeter is the only thing i have fitted.

Would it be worth dropping the Ammeter from the circuit as a test, just to eliminate ?

Wouldnt hurt but I think you have a bad LPS.

i’ll uncouple the ammeter first and see if that improves things if not, it looks like a new LPS :frowning:

Any other tests can be done on the LPS to be sure its that ? Dont mind repacing it, but seems a waste if unnecessary.

There aren’t any more tests that I can think of.

  • We verified that the IN has the correct voltage for full power.
  • The “Test’” button on the supply bypasses all the controls except the IN so the control systems do not seem to be at fault.
  • In all cases the mA meter reads lower than the expected current.

It is not possible to fully rule out your tube as the problem. It could for some reason just not lase at full power even if the LPS voltage is high enough. Since this is a new tube the LPS is suspect.

These supplies are considered consumable. Since they run at such high voltage the components eventually break down and fail. Repairing is not economical because they aren’t that expensive, usually have catastrophic failures, and tinkering with them is dangerous.

So if for some reason we find that the problem is not the LPS :grimacing: you have not wasted your $$$, you will just have a spare.

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