'How to build a two valve set', No 12, Godfrey Philips cigarette card, 1925.
© Science Museum / Science & Society Picture Library
The reverse of the card reads: 'The Earth Terminal Connections. A baseboard mounting coil holder is fitted two inches from the back end and 1/2 inch from the end of the baseboard as shown. The earth (bottom) terminal is then connected to the filament terminal (nearest the back edge of the baseboard) on the first valve holder. A 6in. length of insulated flexible wire is also attached to the earth terminal, the other end of this flex is attached to the split connecting plug, which is supplied with the centre tapped coil (see card 22).'