Teltron tube

A teltron tube (named for Teltron Inc., which is now owned by 3B Scientific Ltd.) is a type of cathode ray tube used to demonstrate the properties of electrons. There were several different types made by Teltron including a diode, a triode, a Maltese Cross tube, a simple deflection tube with a fluorescent screen, and one which could be used to measure the charge-to-mass ratio of an electron.^[1] The latter two contained an electron gun with deflecting plates. The beams can be bent by applying voltages to various electrodes in the tube or by holding a magnet close by. The electron beams are visible as fine bluish lines. This is accomplished by filling the tube with low pressure helium (He) or Hydrogen (H₂) gas. A few of the electrons in the beam collide with the helium atoms, causing them to fluoresce and emit light.

They are usually used to teach electromagnetic effects because they show how an electron beam is affected by electric fields and by magnetic fields like the Lorentz force.