Reviving an old full wave rectifying valve

[Brianc]

100 ohms, 4 volts....

Lawrence.

I don't understand what you mean, Laurence. Perhaps I am being stupid or something!
A 100R resistor across 4V will dissipate .16W (not the value I stated, very simple maths too ).  However, a 4R resistor, 4Watt. This is a lot of energy in a very confined space inside the valve base and it (and the diodes) will get very hot.

Another way of looking at it:
If leaving a winding o/c on a normal mains transformer is bad, how do these general purpose Xfmrs with multi-windings survive in use with only some of the windings used? They do.
If an ordinary mains Xfmr primary is connected to the mains with no loads on its secondaries, does it overheat or fail? They don't.

These are the questions to which the answers suggest that no "load" resistor is necessary.