'How to build a two valve set', No 24, Godfrey Philips cigarette card, 1925.
© Science Museum / Science & Society Picture Library
The reverse of the card reads: 'Connecting up. The slack in the battery cable should be pulled through the hole in the cabinet, and the grid bias plugs inserted in the battery which is fixed to the inside of the cabinet. The red plug is pushed firmly into the socket marked + and the black plug in the fourth socket from the + (positive). The black and red flex will be long enough to reach the floor (on which the 2-volt accumultor usually stands) and the spade terminals are joined to the respective terminals of the accumulator.'