Electron Gun Design - Can Positive Voltage Work?

[chucrut]

Hello,
I have a question about electron guns. I have read a lot, and all designs use high NEGATIVE voltage (-1000v for example). Is possible to use high POSITIVE voltage like this drawing?. Or do you think it will not work this way?
Considering that all the chamber walls are at ground voltage (0v) in both cases

 

[berkeman]

Welcome to the PF.

All commercial TVs and CRTs that I've worked with used a high positive voltage at the Anode/Screen, and the electron gun and first few lens voltages are all down around ground and low voltage. Typical medium size color CRTs use around +25kV at the anode button (which is connected to the internal screen):

https://www.quora.com/How-does-the-...hode-ray-tube-TV-monitor-or-oscilloscope-work

 

[bobob]

No, your way will not work very well. The electrons in the chamber will see the electric field between the anode at 1kV and the chamber walls at ground. The entire reason for setting it up with the cathode/filament at negative high voltage is so that the electrons see the field inside the gun and get accelerated into a field free region.

Note that for the purpose of accelerating the electrons it doesn't matter which way you do it. What you are going to do with the electrons and how efficiently you can do it after leaving the electron gun is what matters. In this case you definitely want the chamber walls tied to ground for saftey reasons if nothing else (or a short to floating chamber walls could be lethal). Since the chamber walls are at ground, you want the anode that way too.

In a crt, the situation is reversed. The "walls" of the crt are glass and therefore an insulator. You don't want to float the filament supply to -50kV just to hold the anode at ground when the anode is totally enclosed in glass. That would be dangerous.