'How to build a two valve set', No 23, Godfrey Philips cigarette card, 1925.
© Science Museum / Science & Society Picture Library
The reverse of the card reads: 'The valves. 2-volt Muliard valves are recommended. The first (detector) is a P M I H F valve. This is shown in position. The valve being placed in its holder is the low frequency amplifier and is a P M 2. The set is now ready to be slipped into its cabinet, and is ready to work when connected to aerial, earth, batteries and headphones.'