The reverse of the card reads: 'The anode connections. Here is shown the high frequency choke ("Ingranic") which is fixed to the baseboard as close to the filament rheostat as posible (without touching). One terminal fo the H F choke is joined to the anode (or plate) terminal of the first valve holder. The anode terminal of the second valve holder may now be connected to the lower of the two phone terminals. All terminals should be screwed up tightly.'
© Science Museum / Science & Society Picture Library