Simple PSU for a few valves

[Ian E G7OLT]

The reason that thyristor power supplies were dropped from domestic TV, was down to x million TV power supplies all turning on at roughly the same point in the +ve half of the mains cycle. This caused the power companies problems and damaged generating equipment by introducing asymmetry into the supply waveform. Effectively, DC was injected back into the grid, causing saturation of transformer cores and overheating. By the end of the 1970s, TV manufacturers had dropped thyristor power supplies in favour of switch-mode.

Switch-mode power supplies that are fed from a full-wave bridge and use higher than mains switching frequencies that are not locked to 50Hz, don't cause the same problems. They're also more efficient and can provide mains isolation, important with so much ancillary equipment connected to the TV nowadays.