🚀 go-pugleaf

This is a *very* potted description. It is beyond a single e-mail to explain
them to any real degree.

VALVE (Triode described for simplicity)

A piece of metal is heated. This causes an "electron cloud" to form around the
metal (called the cathode). A positively charged electrode (anode) is placed
near the cathode and the postive charge attacts the electrons, causing current
to flow. Current will not flow if a negative voltage is put on the anode as it
will repel the electrons. Another electrode (usually a wire spiral) is placed
around the cathode and a (usually) negative voltage is placed on it. As it is
closer to the cathode than the anode, it's electric field (at the cathode) is
stronger than the electric field of the anode. As a result, you can control
the rate at which the electrons flow to the anode with a much small voltage
than the anode voltage. If you put a load between the anode and the power
supply, the voltage across it will vary as the current flow varies and as
larger voltages are involved than in the grid circuit, you can get
amplification.

TRANSISTOR (FET)

Works in a similar way to a valve, the gate's electric field can change the
electron flow through the block of semiconductor material.

TRANSISTOR (Bi-polar)

The transistor has blocks of semiconductor P-type - N-type - P-type or N-P-N.
The circuit voltages are reversed depending on what is used, but the principal
is the same. One of the junctions between the two types of material is used to
control the current flow through the transistor. Unlike the valve or FET, the
control mechanism is based on the current flow through the base to/from the
emitter, rather than the voltage at the base.

Nightjar wrote:

> Could anybody out there tell me how valves and transistors work, please? I
> would be eternally grateful.
>
> Adrian, UK

--
Mark Little                    |  ICQ: 13966098
http://brigadoon.apana.org.au  |  mailto:markl@sa.apana.org.au
"His fingers harping the net-mesh" - The Net Menders, Brian Vrepont.