• Tubes are still used in a variety of electronic circuits.valve image by Aussiebloke from Fotolia.com
  
  Before transistors, all electronic circuits used tubes. Tubes performed a variety of functions, including changing voltage, picking up radio signals or amplifying signals. The 12Ab5 tube is an amplifier, capable of taking a small signal and converting it to a large signal. While tube technology is old, it is still useful in many instances. In 2010, many tube circuits exist, particularly in guitar amplifiers. This is because musicians prefer the sound of tube amplifiers to that of transistor amps.
  
  

Configuration

• The 12Ab5 is a pentode tube. This means it has 5 elements, plus a filament. The filament is the heater part that glows, heating the anode. It has one anode, which releases the signal voltage. It has 3 grids. The grids control the signal. At the end of the signal path is a cathode. The cathode picks up the controlled signal. Its base is circular, with 9 pins. Each pin is connected to one internal element.
  
  

Case Dimensions

• The outside dimensions are a length of 2.375 inches, by a diameter of .8 inches. Its pin length is 1/4 inch. The outer case is made of glass, with metal internal components. The pins have a notch, or open space. This is intentionally designed keyway, so the tube cannot be inserted into the socket wrong.
  
  

Voltages

• The filament, also called the heater, requires a voltage of 10 to 15.9 volts in order to operate. The grid voltages are negative 12.5 volts on the first grid, 250 volts on the second grid and 315 volts on the cathode, also called the plate. All these voltages must be present in order for this tube to operate correctly.