Reviving an old full wave rectifying valve

[Yorkie]

I've just realised that the U10 has a directly heated cathode, hence comments concerning connections to the heater.  Maybe Nick knows this already, in which case apologies for mentioning it but in a directly heated rectifier, the heater and cathode are connected together. Hence, on the heater you have the AC heater Voltage - in this case, 4V, and also, the DC HT output from the rectifier, the U10 being a full wave rectifier, 250 - 0 - 250V.

Some small valve rectifiers (EZ81 etc)  are indirectly heated and can be run from the same heater supply as the other valves in the equipment. Most, however, are either directly heated (i.e. the heater and cathode are one and the same) or the heater is connected internally to the cathode. This avoids the need for very thick heater-cathode insulation. If the heater and cathode are connected then the rectifier needs its own separate heater supply.

Had the rectifier been indirectly heated the diodes would need to go to the cathode pin, but as it is, as has been noted, it needs to go to the heater connected to the rectified DC output to the smoothing cap.

A little sketch attached showing the two arrangements of direct/indirect rectifiers.

Nick's already sorted, but it might be of use to others some time.