Any Hope for an Ar/Kr Ion Tube with a Broken or Damaged Filament?
For a filament that is actually broken – continuity shows open or there is a visible gap – the short answer is no. Unless you are into amateur laser construction, do whatever your favorite religion calls for and give it a proper burial (actually, see below). However, such tubes (intact) or parts like Brewster stems/windows and mirrors may still be useful if you are into home-built lasers. The problem is that in order to sustain the discharge, the cathode/filament must be at the proper operating temperature. Unlike a fluorescent lamp, the arc can’t sustain this. If filament power is lost during operation, the discharge will drop out in a few seconds on most power supplies – and this is hard on the tube. As it cools, the emissivity goes down and the voltage drop sustained at the filament will rise with proportionally increased power dissipation – several hundred watts more than it is designed to support when properly heated. If the power supply has enough compliance range to sustain the
