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.