The 6DR7 is a specific type of vacuum tube (also known as an electron tube or valve). It is a 9-pin miniature double triode with two dissimilar sections, one high-mu (gain) and one low-mu unit.
Function: It was originally designed for use in television receivers as a vertical-deflection oscillator (high-mu unit) and a vertical-deflection amplifier (low-mu unit). It is also highly valued by audiophiles for use in audio preamps and amplifiers due to its "warm and rich tonal character" and low noise.
Construction: It has a T-6 1/2 glass bulb, coated unipotential cathodes, and a 9-pin miniature (Noval B9A, JEDEC No. E9-1) base.
Manufacturer: The 6DR7 was produced by various manufacturers, including RCA, Sylvania, GE, and Tung-Sol. Most available tubes today are "New Old Stock" (NOS), meaning they were manufactured years ago but never used.
Interchangeability: It is also known by the cross-reference numbers 6FD7 and 6FR7.