This set  eliminated the ned for pricey audio coupling transformers featuring direct coupling where the H T  voltage was steped down as it was devided to suit each valve in  turn.  T he other power supply development was the centre tapped choke wherin  the ripple voltage which escaped full supression in the first winding, then resulted in current generated in the second winding, and this ws in oposite phase, resulting in cancelation of all of the first level hum.

What a pity all this was spoiled when someone failed to notice the lack of thr vital locating pin on the base of the rectifyer valv.  Rectifyer valves were at that time almost always positioned by the thick and thin pins reaching  down thru their holes, so there wass only one way reach the correct contact clips on the under side, ( so never a problem )  All they needed was the correct valve. The valve that was required would have a small brass locating pin on its base this pin and the guide grouve  wuuld fave in turn prvented the valve from placing its fillament between the 600Volt AC winding and the first filter capacitor