Reviving an old full wave rectifying valve

[Brianc]

First, identify the mains Xfmr winding wires which go to the heater pins (3 & 4). One pin will have an extra wire on it which leads either to the reservoir cap (or to an input choke). It makes no difference which as the heater pin with the extra wire will be the HT +ve feed. It is to this pin to which the diode cathodes MUST be connected.
I see that you have drawn a 100R resistor from pin 3 to 4. This will dissipate nearly 0.75 Watt so you must use at least a 2W resistor as it is in a confined space - I really don't think that that is a good idea. Lets wait to see what Ed says.