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.
In the amplifier circuitry, diodes may be used to provide a known (approximately) voltage drop where required by the design of the circuit. They can also be used for temperature feedback, although for direct temperature compensation a transistor is more common. These diodes are generally small-signal types like 1N4148. In logic switching, diodes are often used for simple OR-type functions. Look on Wikipedia for diode OR. These are small-signal types. If the amplifier has a switching power supply, or is a Class D amplifier, high speed switching diodes are used extensively.