Every vacuum tube has at least two conducting terminals called
and the "anode".
In action, the cathode is heated to such a high temperature that
electrons, which are speedy to begin with,
gain enough additional energy to break away from the cathode's alkaline
earth metal oxide coating.
This thermionic emission begins as the cathode
begins to glow red. Eventually, a cloud of electrons (negative charge)
in the vacuum surrounding the cathode. At this point, the tube is
ready to go to work.
To open the valve, a high positive charge often called the B+
is applied to the tube's anode, also called the plate. The
plate attracts and collects the emitted electrons,
which are put to work powering your speakers before completing