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/art...cillators.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 pushing 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

"jalbers" wrote in message
...
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/art...cillators.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 pushing 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

Oscillators are the same whether vacuum tube or solid
state, however, if you are interested in vacuum tube
circuits it will be helpful to have some books written when
they were the ones being used. There are several classic
books on electronics at Pete Millett'
s site at http://www.pmillett.com/ ranging from quite
elementary to advanced engineering and theory books. See
http://www.pmillett.com/technical_books_online.htm
Also, the old RCA tube manuals had a very good section
on vacuum tube fundamentals, very much worth reading. This
section did not change much over the years so almost any
edition will do. I think there are a couple on the above
site.
Note that Pete's files are very high quality and VERY
large. If you are on a high speed connection this is no
problem but don't try it on a dial-up:-)


--

--
Richard Knoppow
Los Angeles
WB6KBL

jalbers wrote:
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. snip

Here is an excellent on-line vacuum tube tutorial,
prepared by a retired engineering professor,
Dr. James B. Calvert:
http://mysite.du.edu/~etuttle/electr...t27.htm#Theory

73,
Ed Knobloch