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.
EHX 300B. Russian manufacture. Eight course heater. Directly heated triode.
SOVTEK 2A3 - Power tube. Directly heated Triode - D.H.T. Made in Russia. Typical of the SOVTEK brand, these are built well and sound great.