Somebody told me that a tube would go bad if air would get in? How would that be possible and what would be the effects?

 

The air in a CRT has been evacuated, i.e. it is a vacuum tube. If air were allowed in the electron beam would collide with the air molecules and the CRT would simply stop working.

Air can enter into the CRT if there is a crack in the glass. The most likely place where that can happen is at the base of the tube where the pins emerge or at the neck of the tube where the glass is thinner and more vulnerable to side impact.

 

The air in a CRT has been evacuated, i.e. it is a vacuum tube. If air were allowed in the electron beam would collide with the air molecules and the CRT would simply stop working.

Air can enter into the CRT if there is a crack in the glass. The most likely place where that can happen is at the base of the tube where the pins emerge or at the neck of the tube where the glass is thinner and more vulnerable to side impact.

Also, the filament is extremely hot, which causes the cathode to emit the electron beam. When exposed to oxygen (in the air), the filament will burn out almost immediately.

 

Also, the filament is extremely hot, which causes the cathode to emit the electron beam. When exposed to oxygen (in the air), the filament will burn out almost immediately.

Similar to when you get a crack in an incandescent lamp bulb.

 

You may even be able to see the "getter" flash change in appearance.

http://en.wikipedia.org/wiki/Getter

 

Thanks a lot guys very helpful answers