Was there ever a tube/valve available with an insulated grid?
It would be easy to coat each of the grids in its own glass coating. I just wonder if any one ever tried to make one. It would prevent grid current; make for a very high impedance grid input, even more like the gate in a FET, except a lot more linear. And without that DC bias current running through the grids, they'd have less noise.
Not in this case. The grid intercepts some of the electrons going through the vacuum from cathode to plate which causes a small grid current. Thus his suggestion to add a insulating coating to stop this current.
Not in this case. The grid intercepts some of the electrons going through the vacuum from cathode to plate which causes a small grid current. Thus his suggestion to add a insulating coating to stop this current.
Insulating, not isolating. The grid still has its field effect. No grid current would flow, so the tube would not self-bias.
Ecerfoglio: Yes, tubes contain a vacuum, but current flows through the vacuum from cathode to plate and this current flow is controlled by the field effect (voltage) of the grid(s). After looking at your responses, I can see that you need education about tube theory so that you may opine without embarrassment. Here, read and learn:
Crutschow: You understand. Do you think that any static charge on the glass grid inulator surface would have any effect (like the charge on a glass rod in a high school science lab)?