[Arran]

Jayce:
  With regard to the type #47, or any other early AC tube with a low heater voltage, make sure that you check the actual voltage that the tube tester is putting out, under load, with a digital volt meter. I've had some problems with at least one tester of mine, yes it puts out 1.5 volts but not 1.5 volts at 1.05 amps for a type 26, the same is true of tubes like #45 at 2.5 volts at 1.4 amps and #47s at 2.5 volts at 1.75 amps. Another thing to watch for is that sometimes the solder joints in the tube pins break down building up a high resistance, or sometimes an open connection, I've fixed a few tubes with this problem either on the grid or the filament pins.
Regards
Arran