RF CO2 build

Howdy all.
I wanted to share my build in progress and hopefully get some input from those that have undertaken a build with these RF CO2 tubes before.

For those that don't know, here are some links from my research. I won't explain everything here...i'm close to getting this up and working, but still have some problems and questions.

First the links:
http://laserpointerforums.com/f40/rf-excited-co2-lasers-25113.html
http://laserpointerforums.com/f39/5w-co2-laser-tube-rf-amplifier-150-delivered-23204.html
http://laserpointerforums.com/f43/starwarz-co2-power-47504.html
http://www.photonlexicon.com/forums/showthread.php/6341-Synrad-Laakman-10W-CO2-Laser?highlight=RF+CO2


The following comes with great thanks to all that posted in these threads and shared their triumphs and failures!

First the RF controller board. I had four tubes and no controller board(the ones I saw in others photo's). I was able to find these from an auction(6 boards in one...I had to use a band saw to cut them apart).
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The RF board takes 12V@5A, 5V@~300mA, and 5V on/off(I think TTL).
(i'm not completely sure through my reading if I should jump the 12V connection like I have.)
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the TTL 0-5V connection(at first when I tried to power the board the RF light was not coming on, until I hooked up a 9V battery to this connection...now I have two green lights!)
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This is a photo of the Balance coil/RF transistor assembly...it came with my original tube. This is also where I have some question wether it is hooked up correctly.
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So lastly some photo's of the complete setup. The tube, balance coil, RF board, 36V@10A PSU, 12V@5A PSU, 5V@300mA wallwart, and 9V battery. In the first photo you can see that I did get the two lights to go green and the RF chip does warm up right from start(I haven't let it run long as i'm not getting lasing from this tube yet).
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(Sorry about the blurry on these, just quick photo's of progress, when I get it up and running stead I promise nice clear photo's)
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Thanks for taking and look, hopefully I can get some input from those that have tinkered with these before. There is a chance that one of my tubes doesn't work, if it looks to be that way I think it should be easy enough to plug another in place and try try again.:thanks:

EDIT:....There is a fuse spot and a light on the small (36V) input board. It crossed my mind that perhaps there should be a fuse? The red light has not been lit in my other try's and i'm not sure if that'a a good thing or not. I decided to just try a wire bridge in the fuse ports as I don't have the correct fuse right now. When I tried it again still no lasing but the red light came on. I also tried to hook up two of the other tubes that I have with the same results. I just have the feeling that some small part isn't connected correctly.

EDIT 2:....Geez still working on this and can't see where i'm going wrong. I'v read and re-read all the treads, and all the trouble people have run into. I'm still wondering about the red light, although in working videos I don't see any fuse used or the red light lit. I'v also checked continuity grounds between all the points I read about...grounding the pre-amp, the FET having ground to the laser chassy(the middle pin shows ground, even though the FET isn't directly connected to the tube housing.).......

EDIT 3:.....(thanks to Hemlock Mike for your PM's)......I'm still having troubles getting this fired up....I'm getting the voltage to the amp...around 34V and all lights are on, the RF module on the pre-amp gets warm like it should, but i'm still getting no heat on the FET. Does anyone here know how to test one of these to see if it is malfunctioning?......Hopefully I can get someone to post here!

Yeah, definitely need a fuse on the FET filter board. I think it's a 10A if I remember correctly. I need to see what's going on on the FET side of your HS. Looks like your missing the choke coil needed for it to oscillate correctly. This is the hardest coil to adjust to get it to lase. Also the big coil on the side of the tube. It takes quite a few hours with a nylon prod to get it in tune.

Also, both LED's are lit on your driver board so you should be getting an output from it. You can use a CB power/SWR meter to verify you should be getting about 35W of RF to the FET.

RF CO2 lasers sound like a damn right pain in the @ss

Interested to see it going though.

Things said:

RF CO2 lasers sound like a damn right pain in the @ss

Interested to see it going though.

Click to expand...

Yep, Pumping a laser with RF is basically magic. RF takes all the fundamental principles of DC circuits and throws it off the cliff.

Millimeter lengths of wire or a speck on a solder joint will make or break the gas ionization thus killing any chance of lasing.

I think I'll just stick to my "feed it 10-20kV at a few mA" sealed tube CO2 laser

300EVIL said:

Yep, Pumping a laser with RF is basically magic. RF takes all the fundamental principles of DC circuits and throws it off the cliff.

Millimeter lengths of wire or a speck on a solder joint will make or break the gas ionization thus killing any chance of lasing.

Click to expand...

:cryyy:.......

Well i'm still going to try this one. I have all the parts, most of it seems to be working, 4 tubes that I can try it with(not all may work....that's a nice twist), some extra pre-amp boards(the large one), and a knack of getting through problems.

I'v done all the reading on a DIY setup using these tubes I can find. If you have any more input it would be greatly appreciated. I keep reading people getting these kits and firing them right up and then others spending months trouble shooting them.
Quite frankly I could just get a CO2 40W and PSU from China and be ready to go(although I still want one!), but wanted to undertake something "a bit" more out of my range.

I took very detail photo's of the assembly in question and the main board as i'm a visual learner and have gathered much of my research from photo's.

"I need to see what's going on on the FET side of your HS. Looks like your missing the choke coil needed for it to oscillate correctly"

Here are some photo's....now I did read that adjusting the coil may fix the problem and did some adjusting, but was afraid to go near it when powered up.
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"You can use a CB power/SWR meter to verify you should be getting about 35W of RF to the FET."

Unfortunately i'm still building up equipment and skills for these uses. What I can tell you is the FET does not get warm at all when I power up. I have done a continuity test between the two boards and tested voltage at the pre-amp and input at the laser and everything seems okay.(EDIT: with a quick check I found this for a fair price and seems like it works within the range I need....http://www.radioshack.com/product/index.jsp?productId=2036239&CAWELAID=107590073#)

As for the fuse I actually haven't seen it used in any photo's or this video of a lasing unit.
There is some discussion about it that doesn't seem to go far....here is the fuse in question...
http://search.digikey.com/us/en/products/0251015.MXL/F2352-ND/776752


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The video were the fuse connection is just bridged without a fuse in place.(this is not my laser working yet, the video came from 300Evil on PL)

Thanks for your help, i'll start prodding and adjusting and hoping for that RF magic. Anything else that you can see in the photos that my be off let me know please, I think the album for the photo's should be public.:beer:

i feel like while watching that i should be wearing some kind of eye protection. haha
congratulations on getting it to lase just a little bit so far! keep at it

flare09 said:

i feel like while watching that i should be wearing some kind of eye protection. haha
congratulations on getting it to lase just a little bit so far! keep at it

Click to expand...

I think that video is of 300EVIL's RF CO2 at roughly full power IIRC.

diachi said:

I think that video is of 300EVIL's RF CO2 at roughly full power IIRC.

Click to expand...

It is his video, I did send him a PM on PL asking him to take a look. I do appreciate him dusting off the ol' LPF account. Some of the discussions I read ended in PM's which didn't help me. I like to keep the discussion in the open if possible so other in the future can look it up, and hopefully do some reading before asking a bunch of questions!

Very cool laser :gj: on getting it to work.

So below the round fuse block and blue capacitor under the circuit board
there is something that looks like about 40ea coin cells in a plastic tube ?

What is that a 120 volt battery :crackup:

Thanks Jeff, but I haven't gotten it up and running yet. The video was to show a unit lasing and also that it doesn't seem he is using the fuse but rather just a jumper.

I'll post a video of my own when I get it figured out and running. I'm going to try the adjusting that 300Evil suggested, still not sure why my FET isn't getting warm though. I'm a bit farther along now than others got, and was lucky I think to get the pre-amp going with both lights lit!

Now I just need to figure out if my connections are all okay, if my FET is still working and if the tubes I have work as well.(the tubes 'should' work)


EDIT: WELP the FET is getting hot now! Turns out I didn't have the small board(34-36V input one) grounded to the tube chassy. Now the Fet get Hot...I have it heatsinked, I hope enough. Still no lasing though. This is where it comes down to tweeking or if I have a working tube!

The two green lights mean you are getting good RF power out of your board. The problem is probably the transistor floating off the tube ground. Mount it to the tube and it should fire. The rf pre-amp board getting warm is good, that means your main RF transistor is working. I found the connecting cable should have 50 ohm impedance.

My best guess is the laser tube is not tuned in to your coil (main coil) or the small RF coil needs tuning. FET's usually fail shorted so if it is drawing some current, but not overloading your PS it is a tuning issue. If it is drawing no current there may be a problem with a connection to the RF driver. These transistors are a beast, they can take a lot of abuse.

Let me guess, no oscilloscope?

heruursciences said:

The two green lights mean you are getting good RF power out of your board. The problem is probably the transistor floating off the tube ground. Mount it to the tube and it should fire. The rf pre-amp board getting warm is good, that means your main RF transistor is working. I found the connecting cable should have 50 ohm impedance.

My best guess is the laser tube is not tuned in to your coil (main coil) or the small RF coil needs tuning. FET's usually fail shorted so if it is drawing some current, but not overloading your PS it is a tuning issue. If it is drawing no current there may be a problem with a connection to the RF driver. These transistors are a beast, they can take a lot of abuse.

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Thank you very much for your reply. It will take some time to get through the tuning I think.

The FET is now getting HOT...I have it heat-sinked and put a fan on it for good measure. The real wild card here now is the tube's themselves! I have four tubes total. Three I purchased in an unrelated ebay auction, the seller said one works(I know these things are a gamble), the last tube I got from you in an earlier auction. The tube from you I would give the best chance but it was without a main coil. I have some 14 guage magnetic wire coming but then it will come down to trying to tune TWO coils....the main one on the tube and the secondary small one near the FET.

Is there some way to test that the tube is good? I'v tried a bit of prying and pulling on the small coil near the FET while it was powered but to no avail...again this could be because of the tube itself.

I'm coming up close...I can feel it, can't wait to see........nothing.......except a quick burst of the cardboard catching a'blaze before it hits the beam dump.

EDIT: grenadier...i'm still new to electronics and building up what I can use and understand. I know an oscilloscope will be an investment in the future, but I'm not sure yet how to use one. There is still a lot of reading and learning on my end. Right now most of my work is through the aforementioned reading and magic/luck/prodding around/try-something-else/read-some-more/pixie dust.

532 with Envy said:

EDIT: grenadier...i'm still new to electronics and building up what I can use and understand. I know an oscilloscope will be an investment in the future, but I'm not sure yet how to use one. There is still a lot of reading and learning on my end. Right now most of my work is through the aforementioned reading and magic/luck/prodding around/try-something-else/read-some-more/pixie dust.

Click to expand...

:wtf:

Tektronix 2225 Oscilloscope 50MHz 2 Channel, used | eBay

I suggest you buy this before you fry out some expensive RF transistors!



Also, I have a feeling that somewhere the impedance isn't matched properly. RF circuits are very, very picky.
I also suspect that mosfet met the undertaker.