I am an ex BT employee, joined in 1998 and was buddied up with a lovely old feller who showed me the ropes.
He swore by the old 1985 oscillator over the more modern types. I have the more modern types but recently purchased this off eBay:
I need batteries for the oscillator part of the kit, does anyone know where I can get them? I believe the BT term is cell, dry no2.
The battery terminal is the same type as a standard 9 volt battery, but the positive and negative terminals are further apart.
Even if I knew the correct voltage I could find a modern equivalent I'm sure!