337ND

This page is about making an old LSI thyratron based nitrogen laser work


First, stripping the plasma cartridge

LSI PART NO. 337290 PLASMA CARTRIDGE NO. 135ND




There are four main caps, and two peaker caps, all 440 pF, 20 kV









The tube has windows glued to each end with a few degrees of wedge, and there are external aluminized mirrors mounted in the laser's enclosure.











The HR on its mount.  It is concave with a focal length of about 20 cm. 




The OC is supposed to be a 1/2π wedge, but this one is broken.  Based on my measurements of the HR RoC (40±6 cm) and HR to OC separation (15 cm), the OC RoC should be ≃25 cm for a stable concave-convex resonator, which makes better use of the gain medium than a resonator type having a focus in the tube.


An acrylate enclosure now holds the cartridge contents.  The original tube has been replaced with a refurb, but you can also refill it yourself, which I've done with another cartridge, see here.


A spark from the HV side is jumping to the rim of the spark gap.  I now wrap electrical tape around spark gaps before installing.


Pumping dye


Later the 337ND stopped working with the thyratron.​  The trigger board still clicked but the tube didn't fire.  It started missing a pulse or two, then more, and finally stopped pulsing altogether, just clicking.  Over a couple of minutes.  The HV is ok.  It's just that the trigger section was not translating the clicks into pulses.

A trigger board from amazing1.com replaces the LSI trigger board, thyratron, HV pulse
transformer (black box below trigger board), HV pulse power supply, thyratron heater board, and the fan is not needed.

Only the black HV supply in the upper left is being used.


I haven't taken the unused components out.  The new trigger board is next to the thyratron (with the yellow capacitor).  An inductor for measuring the pulse rate is at the end of the blue wires, covered in red shrink tubing, laying on the cover over the tube.




The inductor for measuring the pulse frequency.














No warmup,  instant start.  Three speeds with frequency display, and remote control.