Grid Leak Bias
A valve/tube has a resistor connected from grid to ground, typically as the only bias component. Thus grid leak current is used to bias the valve. Resistors in the region of 1 megohm were common.
When the grid leak stage had a transformer input, the valve grid connected to one end of the transformer secondary, and the other end of the secondary went to ground via the grid leak resistor and a small bypass capacitor.
The use of grid leak bias competed with use of a so-called C battery for providing a fixed negative voltage on the grid. When vacuum tubes came to be constructed with cathodes electrically isolated from their filaments, it became possible to used cathode biasing. This involved use of a resistor from the cathode to ground, which provides better control of anode current through negative feedback. This method also requires a relatively large capacitor across the cathode resistor to avoid losing AC gain (through negative feedback), and the cost of a sufficiently sized capacitor was an issue in the pre-war years, as capacitors had low capacity per volume and per cost.
Read more about this topic: Grid-leak Detector
Famous quotes containing the words leak and/or bias:
“One leak will sink a ship: and one sin will destroy a sinner.”
—John Bunyan (1628–1688)
“The solar system has no anxiety about its reputation, and the credit of truth and honesty is as safe; nor have I any fear that a skeptical bias can be given by leaning hard on the sides of fate, of practical power, or of trade, which the doctrine of Faith cannot down-weigh.”
—Ralph Waldo Emerson (1803–1882)