300B. A classic DHT (Directly Heated Triode) . Very popular in SET (Single Ended Triode) HiFi Amplifiers as a Power Valve or voltage regulator.
2A3. Power Triode. Four pin UX4 type base. Seen in many Mono Blocks and Class A amplifiers.
SOVTEK 2A3 - Power tube Directly heated Triode - D.H.T. Made in Russia The best currently produced 2A3
EHX ELECTRO HARMONIX 300B Russian manufacture Eight course heater Directly heated triode
EHX GOLD 300B D.H.T. Gold plated grids Eight course heater
GENALEX GOLD LION PX2A3. Made in Russia Gold Pins Heavy gettering The ultimate current production 2A3.
GENALEX GOLD LION PX300B. Made in Russia Gold Pins Heavy gettering Eight course heater The ultimate current production 300B
RCA 2A3 - Pair NOS Blackplate Made in USA Amplitrex tested. Results: B+ 250, VG -43.8 V1 72.6 mA, V2 67.8