The use of a centre-tapped secondary on an inter-valve coupling transformer obviates the need for a valve phase splitter and makes for a considerable economy. The stage as shown above is basic and in practice more components are likely to be found but the ones shown are fundamental to the principle of the transformer coupling method. The left hand triode is a conventional AF amplifier and signals appear on its anode, the primary of the transformer acting as the anode load. C1 and R1 are the usual RF decoupling components. The split secondary feeds out of phase signals to each of the output valve grids, the tapping being in this case returned directly to ground, with the resultant need to bias the output valves in some alternate manner.

Note that the valves in this rather early circuit are of the directly heated type

and have no cathodes. Had these been indirectly heated types the cathodes would be commoned and fed to ground via a bias capacitor in the usual manner but in the absence of cathodes this bias is neatly provided by the heater winding on the mains transformer (T3), which is centre-tapped and would perhaps normally be earthed to chassis but instead is grounded via R2. This means that the output valve grids are negative with respect to the filaments by the amount of the voltage dropped across R2. C2 is a bypass (reservoir) for R2.