Ferranti 6SL7GT. a 6SL7GT valve tested on an AVO VCM Mk3 with very good results, see below. Make: Ferranti. Valve: 6SL7GT. Type: double triode.
RCA 6SL7GT VT-229 Valve, Tube, AVO tested good
Pair 6SL7GT VT-229 Valve, Tube, possibly Ken-Rad , AVO tested very good
Ferranti E-Line Transistor Applications 6th Edition August 1971
Ferranti E-Line Transistor Applications 5th Edition February 1970
Ferranti Radiation Resistant Solar Cells For Space Vehicles 1965