Grid leak

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Grid leak is an inherent operating characteristic of triodes and other vacuum tubes. It is the small flow of current through the grid of a tube into the circuit which feeds the grid. This current is caused by the small negative EMF which is present in all vacuum valves as a result of a space charge within the envelope of the tube. The space charge is part of the thermionic effect, which is the fundamental phenomenon behind all vacuum tubes.

[edit] Use

The grid leak detector was in common use in the 1920s in domestic radio receivers. The grid leak detector stage is a non-linear amplifier, which performs 2, or more often 3 functions.

• Detection: The nonlinearity of the stage produces an AF detected component in the anode load. In this circuit the grid acts like the anode of a diode. Detection takes place in the grid circuit.
• AF amplification: The stage is an af amplifier as well as a detector, thus gives much better sensitivity than a diode detector.
• Reaction: in most cases feedback was added to give reaction (aka regeneration) to boost sensitivity and selectivity further