S
Salmon Egg
- Jan 1, 1970
- 0
Then there's the grid mask, whatever that is... how
come the electrons don't smash into that? How do
they find the holes?
It's a very sparse grid of wires, so most electrons miss, just drift
through the big holes between the tiny wires. If you apply a high
negative voltage, you can force the electrons further from the wires,
crowd them into the gaps betweem, and eventually shut down the gaps
completely.[/QUOTE]
For most receiving tube applications, the control (closest grid to the
cathode) runs with a negative potential with respect to the cathode.
That voltage is a few volts, seldom as high as ten. Minus ten volts
would usually be enough to completely cut of electron flow to the anode.
For power rf amplifiers, there usually is sufficient negative bias on
the control grid to reduce anode current to zero without excitation.
When rf is applied to the grid, the positive portions of the cycle
allows current to flow. Typically, the grid potential is driven positive
through a small portion of the cycle to the extent that there is some
grid current. Anode current flows in pulses. The idea is to use the tube
as a switch to minimize dissipation by trying to keep either the anode
potential or current small. In that respect, transistors do much better.
Bill