GZ37, made by Mullard . Mullard and/or Philips labeled
EL3N Philips Connected as triode this is "the" perfect driver for a 2A3 or 300B SE amplifier, amazing sound.
http://www.single-ended.com/EL3N-se.htm http://www.enjoythemusic.com/magazine/manufacture/1108
RCA JAN CRC-6AS7-G 8-pin octal base twin triode. Black plate, made in 1953