Anyone seen/heard these old Yamaha monitor speakers?

Hey guys,

I just bought these old Yamaha loudspeakers (possibly passive studio monitors) for 20 bucks - I would estimate from the looks that they are from 80's - but I can't seem to find anything about them, so I thought to ask if anyone of you might has seen 'em around.

It says that they are model NS-144, and should be pretty easily identified from the white speaker cone. They are large 2-way speakers with a small steel grille in front of the tweeter, which looks to be a 2" driver. Also located in front is "High Level" adjustment pot. The black cloth grille has no markings and can be easily removed. The front and back are painted black, and the rest is light brown "wood" laminate on MDF. The back plate has serial number, model code and according to it they are Made in Japan. The power handling is 25/50 watts.

So could anyone help me identifying how valuable and from what era these speakers are from? I saw a pair with some small faults going for $250 in German eBay so it wasn't a bad deal I'm sure.

Here's a pic from eBay, let's see if it works.