Russian tube 6P3S REFLECTOR factory, output beam tetrode. Best quality, the sound is nice - authentic vintage tone. Near equivalent: 6L6, 6L6GT, 6L6GC and 5881
Russian tube GU-34B generator tetrode, it is used as a broadband amplifier of HF oscillations at frequencies up to 250MHz and with an output power of at least 400W