grid of a 78E vacuum tube amplifier
Date: 1920-1940
Inventory Number: VT5193
Classification: Vacuum Tube
Subject:
Maker: American ?
Cultural Region:
Dimensions:
0.8 x 3 x 1.6 cm (5/16 x 1 3/16 x 5/8 in.)
case: 4 x 3.6 x 3.6 cm (1 9/16 x 1 7/16 x 1 7/16 in.)
Material:
Accessories: red cardboard cylinder case
Description:
Two metallic rods parallel to each other that hold 30 pairs of thin wires that go from one rod to the other tracing an arch such that a cavity is formed within the two rods surrounded by wires.
Signedunsigned
FunctionThis is the grid of an amplifier. In its original arrangement, there would be some form of cathode, probably a set of tungsten filaments, inside the cavity formed by the thin wires, and the grid itself would be surrounded by an anode, probably a hollow cylinder or pair of curved metal sheets. In operation, there would be a large voltage difference between the cathode and the anode such that electrons flow from the former to the latter. The grid would be set to a voltage even lower than the cathode and be connected to a signal to be amplified. The function of the grid is to prevent some of the electrons from reaching the anode in proportion to the strength of the signal at that instant, with the effect that the signal is reproduced in the electric current flowing from cathode to anode, only much larger than the original signal.