45

The type 45 is a directly-heated triode from the late 1920s, producing roughly 1.5-2W in single-ended Class A. It is widely regarded as possessing the most transparent, pure midrange of any power tube ever made, with a directness that makes 300Bs sound colored by comparison. The penalty is its extremely low power output, demanding speakers of 97dB+ sensitivity. Its 2.5V filament supply and fragile construction make it a tube for dedicated enthusiasts, with NOS RCA, Sylvania, and United Electronics examples being the most prized.