['LIVEWIRE?']

I'd forgotten about BY127's & BY133's, which, IIRC, were/are basically the successors to the BY100 'top hat' rectifiers. In a circuit diagram for a ST-70P PSU 4 x MUR4100 diodes are used, two in series in each 'leg' of the transformer secondary, ahead of the GZ34 anodes. Never heard of the MUR4100, but it presumably has a lower PIV than 1N4007, etc., hence the need for two in series. No doubt I'll opt for the UF series or the BY1xx.
Incidentally, as an 'old hand', I always use the term P.I.V. What's the difference between that and V.R.R.M., which has now been in use for some years?