With the age and delicate filaments of 70 year old battery
valves it seemed a good idea to have some means of checking not
only filament continuity but also filament emission. and working
characteristics. (Also it was something "to do!")
Small and simple was the objective. The answer came in the form
of a device drawing it`s power from existing equipment - a stabilised
variable DC power supply and an AC variac. With these power supplies
the tester is not totally isolated from the AC mains, so some
caution is necessary and the equipment is housed in a wooden insulating
case It could be modified to operate from an existing mains isolated
power supply,but then loses some of it`s simplicity.
The photograph shows a Cossor 220 P on test.
The item beside the unit is a piece of high tech equipment,
a valve base with a torch bulb soldered in, much safer than an
elderly valve for a first switch on.