Get On Board with. Compass Card. Compass Card is the smart card and smart choice for transit passes in the San Diego region. Compass Card is your ticket for the Bus, TROLLEY, COASTER, and SPRINTER.ompass Card. Compass Card is the smart card and smart choice for transit passes in the San Diego region. Compass Card is your ticket for the Bus, TROLLEY, COASTER, and SPRINTER.
Electron (or Vacuum) Tubes. An electron tube (also known as a 'Vacuum tube', or a 'Valve' ) is a glass or metal enclosure in which electrons move through the vacuum or gas from one metal electrode to another. The vacuum tube is often used to amplify weak currents or act as a one-way valve (rectifier) for electric current. Before the 1947 invention of the transistor the electron tube was the basis of virtually all electronic devices. The simplest kind of electron tube is the diode, which was invented in 1904 by John A. Fleming.
A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material with a pân junction connected to two electrical terminals.A vacuum tube diode has two electrodes, a plate (anode) and a heated cathode. Semiconductor diodes were the first semiconductor electronic devices.he most common function of a diode is to allow an electric current to pass in one direction (called the diode's forward direction), while blocking current in the opposite direction (the reverse direction). Thus, the diode can be viewed as an electronic version of a check valve.