I want to do some experimenting with vacuum tubes. I can remember
being fascinated by them when I was a kid. As I got older I became
interested in solid state electronics, turning my back on tubes. I
find that the older books are easier to understand and seem to fill in
some of the gaps that newer books leave out. Most of the circuits in
the old books are based on vacuum tubes. Right now I am interested in
really understanding how oscillators work. I want to begin with the
Armstrong oscillator. Consider the circuit at:
http://www.electronixandmore.com/articles/oscillators.html
I get the basic idea about the tank circuit creating a decaying sine
wave at a frequency determined by L and C and the tickler coil kicking
in at just the right time (I am assuming at the positive peaks of the
sine wave?) kind of like pu****ng a kid on a swing.
I don't understand the how the grid resistor and grid capacitor work.
I am having trouble understanding the statements:
"The grid resistor drops the voltage, thus the grid is very negative
with respect to the cathode. The grid capacitor keeps enough charge to
keep the grid negative for at least one cycle of oscillation, it helps
keep the grid negative when either side of the LC circuit is positive.
"
I need some more explanation. I understand that the triode is passing
the most current when Vg = 0 and passing less and less current when Vg
goes more negative.
Any help would be greatly appreciated. Thanks
