This is the original
1968 predecessor to the Sugden A21
Versions of the A21 have been on sale ever since and
can still be bought today.
Essentially it is still the same pure Class A solid state design that has been refined over the decades. (Although the modern incarnation starts at about £1650)
You will doubtless get interest from collectors. If using it yourself I would suggest
calling Sugden and getting advice on where to have it serviced first.
A recent sale of a (Sugden version) A21 of the same vintage got £147 on ebay uk (
Link) despite being a bit tatty.