'How to build a two valve set', No 22, Godfrey Philips cigarette card, 1925.
© Science Museum / Science & Society Picture Library
The reverse of the card reads: 'The Inductance Coil. The inductance coil shown is a No 60 (Edison Bell Radio) centre tapped. The plug on the short flexible lead from the earth terminal is plugged into the socket as shown. With the average serial the tuning range will include most of the broadcast wave band. For 5XX and Radio-Paris stations, a coil No 250 will be required. This also must be centre tapped.'