Low-frequency output tetrode 6P1P-EV tube. Great sounding! Near equivalent: EL82, and similar to the 6AQ5, EL90, 6V6. Different pin out (9-pin base versus 7-pin base) than an 6AQ5 / EL90
Russian tetrode tube GU-74B are direct replacements for use in some of the best-built RF power amplifiers, including Alpha 99, 91B, 8100; ACOM 1000, 1006, 1010, 2000A. Fully equivalent to the modern 4CX800A tube
Russian electron tube 6P3S-E REFLECTOR factory, output beam tetrode. Best quality, the sound is nice - authentic vintage tone. Near equivalent: 6L6, 6L6GT, 6L6GC and 5881
Russian tetrode tube GU-74B are direct replacements for use in some of the best-built RF power amplifiers, including Alpha 99, 91B, 8100; ACOM 1000, 1006, 1010, 2000A. Fully equivalent to the modern 4CX800A tube