so here are the pics of my lovely wee girlfriends first bass... she had it for 20+ years, unplayed. Its beaten n battered. Just adjusted the neck and still the bridge to do. Check out the dodgy Erth and ground wires... its a real cool bass to play but needs some work done to it. Going to open it up and have a look inside. Ive never heard of 'Diamond' and cant find anything online on such a bass. 766537 serial.. could it mean made in 76 ? Ive no idea. Anyway... a project for me this winter!
"Diamond" guitars and basses - mostly in Les Paul shape - were dime-a-dozen in some parts of Eastern Europe back in the late 70s and very early 80s. Some of them had an in-built booster/fuzz. I've never played their version of Jazz Bass, but have seen a P-Bass or two in those dim, dead days of my teenage years. Inexpensive but fairly serviceable instruments in my recollection. Your serial-related-presumption is likely a correct one. Have fun with it.