'How to build a two valve set', No 1, Godfrey Philips cigarette card, 1925.
© Science Museum / Science & Society Picture Library
The reverse of the card reads: 'The circuit choosen for this efficient two valve reciever incorporates a well known Hartley method of applying reaction which is controlled by a small variable condenser. The cost of the materials is under £3, but by substituting cheaper components the price can be reduced to about £2, without seriously reducing the efficiency. This cost does not include headphones, valves and batteries. All components actually used in the set described are of the highest quality and are thoroughly recommended. The set is easily constructed and no soldered joints are necesary.'