Firebottle

/fī(-ə)rbä-tᵊl/
n. A large, primitive, power-hungry active electrical device, similar in function to a FET but constructed out of glass, metal, and vacuum. Characterized by high cost, low density, low reliability, high-temperature operation, and high power dissipation. Sometimes mistakenly called a 'tube' in the U.S. or a 'valve' in England; another hackish term is glassfet.