Anyone know how to create an electronic KN2 tube ?

[heroic]

Heroic wrote:
I do know that krytrons *are* still used- they combine being very fast and repeatable with being resistant to overvoltage, EMP and other such nasties- but you're going to have a heck of a time finding one.
end quote

Uncle sam and Uncle Ivan both now hire expensive contractors to make reproduction tubes. There are 3-4 companies that do no nothing but run old vacuum tube lines as one offs, very quietly,and very expensively, for Uncle. Some of the big projects, like linacs, have went to refurbing their own big RF tubes.

There are a couple of other places these things are used, but you're right- the little ones are increasingly replaced with high-tolerance semiconductors. (The last place I saw a krytron used was actually in a big Xerox litho machine- it was used to fire a strobe there, too.)

For the specific application here I'd suggest an SCR (thyristor), one of the scary fat doorknob ones, with a pulse-forming network on the trigger and something to sharpen up the output pulse a little (high current Schmitt diode?) and you're golden.

[Vaporware]

For the specific application here I'd suggest an SCR (thyristor), one of the scary fat doorknob ones, with a pulse-forming network on the trigger and something to sharpen up the output pulse a little (high current Schmitt diode?) and you're golden.

Great to hear. Got any suggested part numbers ? Might be a challenge to fit it in the same space as a KN2 but it is worth a try. They did not leave much room on that PC board. That was one feature of the KN2. Really small footprint. Guess I could try to make a new PC board.
So far I have not heard back from the two companies that I made inquiries about a replacement for the Krytron KN2. Both companies have web pages that indicate they have semiconductor solutions for a Krytron tube. I suppose they forwarded my interest about a Krytron to others for a little bit of investigation. Might get that 'knock on the door' next week.

Later,
Tom

[heroic]

Great to hear. Got any suggested part numbers ? Might be a challenge to fit it in the same space as a KN2 but it is worth a try. They did not leave much room on that PC board. That was one feature of the KN2. Really small footprint. Guess I could try to make a new PC board.

The problem is going to be inductance. To get the rated pulse energy from the laser, the rise time of the pulse to the strobe has to be exactly correct. If you have to make the PCB bigger, the inductance of the traces is going to change and you may need to recalibrate the system. I don't know if this sort of calibration is possible for your equipment...

[Vaporware]

The problem is going to be inductance. To get the rated pulse energy from the laser, the rise time of the pulse to the strobe has to be exactly correct. If you have to make the PCB bigger, the inductance of the traces is going to change and you may need to recalibrate the system. I don't know if this sort of calibration is possible for your equipment...

Yes. It is going to be a challenge. I seem to have conflicting information from the Korad reference manuals. In one manual the specs on the system are stated: Pulse energy 30-60 joules, Optional 150 joules, Pulse width 500 usec, beam size 3/4 inch. In another manual the K2 head specs are listed as : Repetition rate @ 10,000 Joules/shot - 3 per min, Cooling water - 2 ga/min, Energy to lamp - 25,000 joules max, Voltage to Lamp - 10 KV Max, Flashlamp trigger mechanism - Series Injection.
We typically only run the laser around the minium firing theshold of 7 KV so that helps prolong the lasers life.
There are some graphs in the manual as well as the more detailed description of the firing process. On one graph the lamp current waveform appears to max at 200 microseconds than rapidly falls off.
From reading the firing description it states : 'Simultaneously, with the application of the trigger pulse, the ignitron is made to conduct, thus applying the bank voltage to the flashlamp. The capacitor bank is discharged through the ionized lamp, producing a flash of light which optically pumps the rod. As the lamp fires, the current rise rate is limited by the saturated inductance of the injection trigger transformer."
Of course the trigger tansformer is triggered by the KN2 according to the schematic. Yes. This is going to be a challenge to measure all these voltages to figure out the correct parts to use for a replacement of the KN2.

Later,
Tom

[Vaporware]

I did get a reply today from Behlke Power Electronics in Germany. Of course he wants me to get all the operating specs for the tube while it is running. This sounds like I might get to be in the running for the Darwin Award

[heruursciences]

Krytrons are nice for some things such as high speed strobes, but are truly sucky for multipulse use. They quit using krytrons for nukes in the 1990's and now use fiber coupled pulsed laser arrays which are both much more accurate and a lot safer. As for knock on your door, well it ain't gonna happen unless you do something stupid like send them to certain countries abroad, or list them on ebay to the highest bidder, at which point you DESERVE a knock on your door.

As long as your laser does not use the krytron for a EO q-switch and is only using it for the lamp triggering you can get away with using a fast SCR in it's stead. Just be sure to use a pulse coupling transformer and a freewheeling diode unless you feellike blowing up a lot of fairly expensive SCR's. If you can email me the schematic for your laser of the part that has the krytron, I can show you where to put the parts. I also have a lot of SCR's too

FWIW, Your symptoms indicate that the anode is sputter shorting to the trigger electrode, and it is a terminal condition of your krytron. If you have a krytron that used KR-85 as the priming isotope it can be repaired by gluing a radium watch hand to it or wrapping a strand from an unused thorium lantern mantle arround it.

[Vaporware]

If you can email me the schematic for your laser of the part that has the krytron, I can show you where to put the parts. I also have a lot of SCR's too

FWIW, Your symptoms indicate that the anode is sputter shorting to the trigger electrode, and it is a terminal condition of your krytron. If you have a krytron that used KR-85 as the priming isotope it can be repaired by gluing a radium watch hand to it or wrapping a strand from an unused thorium lantern mantle arround it.

Private email sent to you asking for your email address to send the schematics.

Yes the KN2 tube is dying. Was running the system last week and when the system got to a minimum firing threshold it would auto fire even though it had not gotten to the set voltage which was around 400 volts higher. After about four shots it started working again but I am sure that it will start missing again. The KN2 uses a nickel isotope so it is terminal condition.

Thanks, Tom

[300EVIL]

I also have a lot of SCR's too

Hmm... I wonder where you got your stock?