A grid-leak detector is a thermionic valve (UK, Australia, NZ etc.), or vacuum tube (USA), circuit used in older vacuum tube AM radio receivers, which served as a combination amplifier and detector (rectifier) to extract the audio signal from the modulated radio frequency signal.
 The tube used a grid leak circuit to generate the DC grid bias voltage necessary for proper operation from grid current that occurs in all vacuum tubes due to electrons attracted to the grid during the positive part of the RF cycle.
The Fleming valve, also called the Fleming oscillation valve, was a vacuum tube (or "thermionic valve") invented in 1904 by John Ambrose Fleming as a detector for early radio receivers used in electromagnetic wireless telegraphy.
 It was the first practical vacuum tube and the first thermionic diode, a vacuum tube whose purpose is to conduct current in one direction and block current flowing in the opposite direction.
 The thermionic diode was later widely used as a rectifier — a device which converts alternating current (AC) into direct current (DC) — in the power supplies of a wide range of electronic devices, until beginning to be replaced by the selenium rectifier in the early 1930s and almost completely replaced by the semiconductor diode in the 1960s.
 The Fleming valve was the forerunner of all vacuum tubes, which dominated electronics for 50 years.
 The IEEE has described it as "one of the most important developments in the history of electronics", and it is on the List of IEEE Milestones for electrical engineering.
The RCA BIZMAC was a vacuum tube computer manufactured by RCA from 1956 to 1962.
 Although RCA was noted for their pioneering work in transistors, RCA decided to build a vacuum tube computer instead of a transistorized computer.
 It was the largest vacuum tube computer of its time in 1956, occupying 20,000 square feet of floor space with up to 30,000 tubes, 70,000 diodes, and 35,000 magnetic cores.
Sir John Ambrose Fleming FRS (29 November 1849 – 18 April 1945) was a British electrical engineer and physicist.
 He is known for inventing the first thermionic valve or vacuum tube.
 He is also famous for the left hand rule (for electric motors).
 He was born the eldest of seven children of James Fleming DD (died 1879), a Congregational minister, and his wife, Mary Ann, at Lancaster, Lancashire and baptised on 11 February 1850.
Elmer Tiling Cunningham (September 1, 1889 – June 14, 1965) was an American entrepreneur and businessman, specializing in vacuum tubes and radio manufacturing.
 He is best known for being the most successful business person to produce counterfeit (AKA bootleg) or unlicensed vacuum tubes (1915-1920).
 Cunningham was in direct violation by infringing on the Fleming and De Forest vacuum tube patents.
 Unlike other businesses making unlicensed or bootlegged vacuum tubes, Cunningham was very aggressive in his advertising.
 Manufacturers of counterfeit vacuum tubes generally ended their activities after a lawsuit has been filed but Cunningham came out ahead after various lawsuits brought against him and his company, the Audio Tron Sales Company.
 His successes encouraged many others to do the same thing.
The Audion was an electronic amplifying vacuum tube invented by American electrical engineer Lee de Forest in 1906.
 It was the first triode, consisting of a partially evacuated glass tube containing three electrodes; a heated filament, a grid, and a plate.
 It is important in the history of technology because it was the first widely used electrical device which could amplify; a small electrical signal applied to the grid could control a larger current flowing from the filament to plate.
A triode is an electronic amplifying vacuum tube (or "valve" in British English) consisting of three electrodes inside an evacuated glass envelope: a heated filament or cathode, a grid, and a plate (anode).
 Developed from Lee De Forest's 1906 Audion, a partial vacuum tube that added a grid electrode to the thermionic diode (Fleming valve), the triode was the first practical electronic amplifier and the ancestor of other types of vacuum tubes such as the tetrode and pentode.
 Its invention founded the electronics age, making possible amplified radio technology and long-distance telephony.
 Triodes were widely used in consumer electronics devices such as radios and televisions until the 1970s, when transistors replaced them.
 Today, their main remaining use is in high-power RF amplifiers in radio transmitters and industrial RF heating devices.
 In recent years there has been a resurgence in demand for low power triodes due to renewed interest in tube-type audio systems by audiophiles who prefer its sound.
In electronics, the dynatron oscillator, invented in 1918 by Albert Hull at General Electric, is an obsolete vacuum tube electronic oscillator circuit which uses a negative resistance characteristic in early tetrode vacuum tubes, caused by a process called secondary emission.
 It was the first negative resistance vacuum tube oscillator.
 The dynatron oscillator circuit was used to a limited extent as beat frequency oscillators (BFOs), and local oscillators in vacuum tube radio receivers as well as in scientific and test equipment from the 1920s to the 1940s but became obsolete around World War 2 due to the variability of secondary emission in tubes.
The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field while moving past a series of open metal cavities (cavity resonators).
 Electrons pass by the openings to these cavities and cause radio waves to oscillate within, similar to the way a whistle produces a tone when excited by an air stream blown past its opening.
 The frequency of the microwaves produced, the resonant frequency, is determined by the cavities' physical dimensions.
 Unlike other vacuum tubes such as a klystron or a traveling-wave tube (TWT), the magnetron cannot function as an amplifier in order to increase the intensity of an applied microwave signal; the magnetron serves solely as an oscillator, generating a microwave signal from direct current electricity supplied to the vacuum tube.
Tube sockets are electrical sockets into which vacuum tubes (also known as valves) can be plugged, holding them in place and providing terminals, which can be soldered into the circuit, for each of the pins.
 Sockets are designed to allow tubes to be plugged in in only one orientation.
 They were used in all tube electronic equipment to allow tubes, which failed relatively frequently, to be quickly tested and replaced.
 In the day of tube radio and television it was common in the US for local drug stores to have vacuum tube testers, and sell replacement tubes.

Question: Elmer T. Cunningham infringed on the vacuum tube patent of the British electrical engineer and physicist, born on what day?
Answer: 29 November 1849