In electronics, a micropup is a style of triode vacuum tube (valve) developed by the British General Electric Company (GEC) during World War II for use at very high frequencies such as those used in radar.
The VT90 was much more widely used in a broad variety of radars operating in the 1.5 m band, around 200 MHz, which remained in widespread use for the rest of the war.
Key to the micropup design is the development of methods to seal glass directly to metal, allowing the construction of mixed-material vacuum chambers.
The micropup's large physical dimensions would normally result in a low-frequency tube, but this was overcome by operating at very high voltages to speed up the motion of the electrons.
This greatly reduced the length of the glass tube and metal post holding the grid, resulting in a stronger design, allowing it to use a larger cathode and to place the components closer together.