Tung-Sol.com:: FAQs What is grid leakage?

FAQs

Question:
What is grid leakage?
Answer:
Grid leak is the small current through the grid of a vacuum tube into the circuit feeding the grid. It is an inherent operating characteristic of triodes and other multi-grid vacuum tubes. This current is caused by the small negative voltage present in all vacuum tubes as a result of a space charge within the envelope of the tube. This space charge is part of the thermionic effect, which is the fundamental phenomenon behind all vacuum tubes.

Grid leakage is also a term that is frequently incorrectly used to describe the condition of a tube when tested on a tube tester. The correct term is inter-electrode leakage, which refers to leakage paths between the elements of a tube. Many emission type tube testers have leakage tests that far exceed the application of the tube being tested and will reject many perfectly functional tubes. Sencore sold tube testers in the 1960s that were claimed to have the "most sensitive leakage test in the industry".