Thanks for that, Phil. When I'm at one of these sales and am tempted to buy something that I don't really need and that may have no real use, the excuse that I make to myself is that at least it will be useful for spare parts. The reality is that the item often doesn't get used for parts and becomes part of the collection. It certainly seems to be very rare as I could find nothing about it when I did a google search, other than a mention of a similar type of Nashton unit, not a VVM, offered with other items in the for sale section on here several years ago - I think Ed Dinning claimed it. The funny thing was that this type of item usually sells for a quid, but I was surprised to see someone else stick their hand up for a quid, so I had someone bidding against me and ended up paying £4 for it! It was, however, announced and correctly described as a valve voltmeter and perhaps the other bidder had ideas that it might have some useful valves inside. Anyway, it's unlikely that it will be broken for parts, especially as you've asked me not to
I don't need any ECC83 valves for anything at the moment as I've already got plenty and I'm rather more of a valve hoarder than a valve seller. Actually, I don't think I've ever sold a valve, other than in the course of a chargeable repair. That valve coding seems very random to me. It looks like the code on these particular valves indicate the Blackburn factory and possibly made in May 58, 68 or 78? I'll have to start checking all the other Mullard ECC83 etc. valves that I have and see if I can make anything of this coding system.