Anyone know how to create an electronic KN2 tube ?

[Vaporware]

Greeting all. First post.
Got a problem with an old Kolrad K2 Yag 3/4 beam laser system at work that I try to keep alive. The problem is with the EG&G KN2 Krytron tube (http://en.wikipedia.org/wiki/Krytron). The tube is used to trigger the high voltage for the 20K pulse for the large flashlamp. After a time the tube wears out and will not wait for the trigger signal to fire but will instead fire at random charge levels. Not good. Perkin Elmer purchased the EG&G division that produced the tube then shut down the plant about ten years ago. These tubes appear to be impossible to find now so I was looking at any way to create an electronic version of a KN2 tube. Any suggestions ?

Thanks,
Tom

[buffo]

Welcome to PhotonLexicon, Tom! Hope you like it here.

I'd suggest you get in touch with MixedGas here on PL. He should be able to point you in the right direction. Oh, and how about a couple pictures of that beast? (We like pictures!)

Adam

[mixedgas]

Replied to off list

Steve

[Vaporware]

Hi Adam,
I can take a couple of pictures. Wish I had taken a few when I had apart for repair awhile back. It is your typical Yag laser but with a hugh coiled flashlamp. The beast is fairly old. Around 1970's vintage. It takes up a full rack mount case with the high voltage supply in the top section and large capacitors in the lower section. There is a large ignitron tube (http://en.wikipedia.org/wiki/Ignitron) in the lower section with the KN2. The system uses a water chiller for cooling the head which is separate. It gets fired around average 30-40 times a day for a measurement process at work. Although the power supply goes up to 10,000 volts we run it at the minium firing theshold of 7,000 volts. We also had a working Kolrad K1 (smaller with 1/2 Yag beam) which I had to steal the KN2 tube off of to keep the Kolrad K2 running. The K1 and K2 power supply systems are mostly identical. I would like to create an electronic solution for a KN2 if possible to keep both systems running since the KN2 tubes are no longer available new.. I was thinking along the lines of a IGBT replacement but I have limited knowlege in the high voltage area with the exception that forgetting to discharge the high voltage caps of a laser can really hurt your ass when it is hitting the ground. I do have full schematics on both Kolrad systems so that can help and is what I have been using for keeping them running. I am sure that more modern laser systems have electronic solutions but without schematics of a new system I am at a loss of the direction to attempt.

Thanks for pointing me in a direction.
Tom

[buffo]

No problem Tom... Looks like Steve (MixedGas) sent you a PM while you were posting. I'm sure he can suggest a more modern substitute for that Krytron tube.

Sounds like quite the beast though. Do you use the raw 1064 nm output from the Yag for the measuring process, or do you freqency-double it to get green? Just curious...

Adam

[Vaporware]

No problem Tom... Looks like Steve (MixedGas) sent you a PM while you were posting. I'm sure he can suggest a more modern substitute for that Krytron tube.

Sounds like quite the beast though. Do you use the raw 1064 nm output from the Yag for the measuring process, or do you freqency-double it to get green? Just curious...

Adam

Hi Adam,
We use the raw 1064 nm output although for one test fixture we use a copper sulfate solution to decrease the beam power. The other test fixture is inside a 2000 C furnace and we use the raw power of the laser set at around 8,000 volts for increasing the face temperature of a 1/2 inch sample inside the furnace. Another test fixture we use a 1/2 inch square sample which requires the full 3/4 beam size to fully radiate the sample out to the square edges. The system is not q-switched but we do have a q-switch attachement that we have used on the K1 system for a project. Surprisingly the systems have held up very well. The high failure point is the high voltage connector to the flashlamp that attaches to the metal casing of the laser head and is in contact with the di-ionized water. The other high voltage connection that sometimes fails is in a special cell that has dielectric fluid. Did have one bit of excitement years ago on the K1. The new tech running it thought that the cooling fluid was low so he added tap water. It worked for awhile until the dielectric fluid seal broke down and tap water got into the cell. Instant steam generation on the next laser shot and the tech had to clean his underwear. Of course it pretty much destroyed the rod and the lamp. Now we make sure maintaince is done by someone that has a clue.

Tom

[heroic]

Krytrons are tricky; they are monitored technology under several different categories, notably because they are used in time-domain radar pulse generation and in the detonator circuitry of nuclear weapons!

The high speed performance is available from SiGe FETs and the high power performance is available from IGBTs, but it's really hard to get both at once. I suspect that the best solution might be to dig up some NOS parts... these relatively small krytrons were used in some copy machines back in the flat-plate era.

[helium]

I remember successfully replacing Krytron tubes with the electronic type many years ago on Control Laser YAG's used in laser trimming. The Krytron tubes had a label with a radioactive symbol displayed on them and I once heard of a laser service engineer who spent a period of time in an Israeli jail as he was found to have one of these tubes in his toolcase while entering the country.

[Vaporware]

I remember successfully replacing Krytron tubes with the electronic type many years ago on Control Laser YAG's used in laser trimming. The Krytron tubes had a label with a radioactive symbol displayed on them and I once heard of a laser service engineer who spent a period of time in an Israeli jail as he was found to have one of these tubes in his toolcase while entering the country.

Helium & Heroic,
You are correct. The Krytron is a controlled item. Apparently if you have enough of them they produce a detectable signature which tends to get certain governmental agencies to take a closer look. I found this out from a supplier that had around 50 in stock at one time and the goverment made them get rid of them all since they kept setting off monitoring equipment.
I found it interesting talking to a Perkin Elmer Rep awhile back. P&E closed and destroyed the manufacturing line without doing enough research for supply and demand. Apparently one major cost and hassel was with the special controls for the nickel material used. They failed to realize how many Krytron's were used for many different governments around the world in special projects and that most governments have a policy for cyclicing out old stock even if it had not been used. The Rep told me they would be making a killing sellings these now. Hindsight.
I am sure I will find a solution. I think at the time of building these laser systems they used what was on hand and cheap. The world was a more stable place and it was not as much of a security concern. I see a hand written note in the repair manual that it cost $ 43.00 back in the late 70's. When I did get one in 1998 I think it was around $ 450.00. That was before EG&G purchased P&E and change it's name to P&E in 1999. It was also before other events changed the world stability. Now I wish I purchased 4 or 5 of them. It is sad because I need one for a benign purpose that keeps a small business running. A small business that could not afford a new laser system this size but requires a laser this size to do the work. No laser, No work, No need to employee people running it. It is interesting how one small little part can create a domino effect. Luckily the laser is still working now with a burp now and then but I know "Murphy" visits us often.

Later,
Tom

[mixedgas]

Krytrons are not the only trigger tubes out there, Philips made some that are almost as fast without the Ni-4.

what I could find on the web:

ie Z70U AND Z70w

but only 250V of holdoff.

here half way down the page.

http://frank.qe06-50.org/other/Philips/index.html

Considering there are other ways to trigger a bomb, I always thought the krytron thing was used as bait. Start a rumor about this somewhat obtainable bomb part and see who shows up.

There are 2 UK laser companies that used krytrons, and I've seen assemblies show up that had solid state replacements. I worked on a double pulsed ruby that had two KN4s in it,

I just shipped a surplus yag head about 3 months ago that had one.

You can replace the Ni-63 isotope with a small secondary discharge in the bulb, that creates enough ions to get things going.

http://www.electricstuff.co.uk/sparkgaps.html

Send me a schematic in pdf , and you did get my email about Behlke and avalanche transistors?

www.behlke.de


I also know older EG&G microflash systems have krytrons in them. Had one in my lab.

Steve