Hi,
I forgot, Season's Greetings, gents.
Klaus, you may be right; and, to continue the analogies, an apt saying is: "A bad workman blames his tools", and here I am. I have read the Zener datasheet more than once.
r.e. Zeners I don't "hate" them, I'm just extremely prejudiced against them. I haven't found all the above you both say in practice. e.g. the 5.1V 1N5338B goes from 4.85V to 5.36V and I must have been doing something wrong with it because it needed a large amount of current to regulate within those parameters and a large dropout voltage to operate when I tested it. I'll have another go to check I wasn't doing anything odd and I'll be back...
I can't be bothered looking for it, so maybe I'm making this up, but I am certain there is even at least one thread on this forum that discusses the far from ideal qualities of Zeners.
Very witty, Brian, any old MOSFET or BJT would do ( I bought those logic level MOSFETs and subsequently found their app note). It had occurred to me about the relay back emf but as it's not doing any harm, the relay's tiny I would say... The (transformer) supply is a 15V AC secondary that feeds the regulator.