Williamson said there "is no exact equivalent for the Osram type KT66, and its use is recommended where possible. When the equipment is to be used overseas, the KT66 may be difficult to obtain, and the 6L6 glass and metal types may be regarded as direct replacements, with the proviso that the total anode and screen dissipation should be reduced from 25 W to 21.5 W by reducing the total current from 125 mA to 110 mA by adjustment of R21."[6]
Follow-up articles in Wireless World from October 1949 to May 1952 included circuits for Tone controls, Radio Feeder Unit, and modifications for High-impedance Pickups and Long-playing record equalisation. The valves used are: