'How to build a two valve set', No 17, Godfrey Philips cigarette card, 1925.
© Science Museum / Science & Society Picture Library
The reverse of the card reads: 'The L F Transformer. The L F (low frequency) transformer, a Ferranti A F 3, has now been fixed between the two wire holders and clear of the filament wiring. The terminal marked 'Plate' is wired to the free terminal of the H F choke. The terminal on the transformer which is makred 'Grid' is connected to the grid terminal of the second valve holder. This completes the wiring with the exception of the battery leads, which are of insulated flexible wire.'