Simple PSU for a few valves

[glowinganode]

My two-pennyworth.....

A homemade thyristor supply will produce variable voltages, but the switching speed is quite fast, so you get a sharp "edge" to the waveform.

I guess some of the benefits of thyristor control include high slew rate and lower drive power requirements.
Ok till it commits suicide and goes short circuit.
Actually not really ok as the chopped, half-wave rectification makes a right old mess of the mains supply waveform.
Rob.