Hobbies And Interests
Electrical
The 813 has a thoriated tungsten filament, consisting of a tiny amount of thorium added to tungsten, which produces electrons more efficiently than tungsten alone. In addition, thoriated filament has a long life and continues to work under high voltages. The 813 operates on 10 volts, and has a transconductance of 3750 micro-ohms. The greater the transconductance, the more the vacuum tube can amplify. The direct interelectrode capacitances -- the amount of electrical energy a device can store -- for grid to plate with shielding stands at 0.2 pico-farads, with an input of 16.3 pico-farads and output of 14 pico-farads.
Mechanical
The 813 measures 7.5 inches long by 2.563 inches in diameter, and weighs 8 oz. Mounted either vertically with the base up or down, or horizontally with the electrodes' plane oriented vertically, the mount requires spacers to allow a blower to force cooling air under the vacuum tube and prevent overheating. The 813, as a tetrode vacuum tube, contains four active electrodes -- the two filaments to emit electrons, the control grid to vary current in the tube, and the screen grid to isolate the control grid from the beam forming plate. The control grid stays isolated from the plate to prevent the capacitance between the grid and plate from appearing larger than it truly is, in what's called the Miller effect.
Pin Connections
The 813 has seven pins numbered clockwise while looking at the tube from the bottom with the gap between the pins oriented up. The first pin to the right of the gap, a filament connection, emits electrons. Pin two stays unconnected, as does pin six. Pin three, as the screen grid, connects to external positive voltage. Pin four -- the control grid -- modulates the current. Pin five serves as the beam-forming plate used to focus the electrons. Pin seven, another filament connection, also emits electrons.