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2A3 / 300B / 811 / 572

2A3, 300B as well as SV811 and SV572 are directly heated triode (DHT) tubes.

2A3 Tubes

RCA introduced 2A3 in 1932 as a low-frequency amplifier tube. Today 2A3 is often found in the output stage of single-ended audio amplifiers. Despite its relatively low output power of 3.5W, 2A3 delivers that magical sonic signature unique to a directly heated triode tube.

300B Tubes

Western Electric introduced 300B for phone audio amplification in the telephone system in 1938. 300B outputs 10W in a single-ended configuration. 300B delivers smooth and natural sound, especially when coupled with high-efficiency speakers.

SV811, SV572 Super Triodes

Svetlana SV811 and SV572 tubes are high output triodes. With Thoriated Tungsten filament and no getter, these tubes have a unique look. These tubes are the ultimate final evolution of audio triodes, and very deserving for special DIY audio amp projects with high aspirations.