koss 4AA Headphone`s

Hello All.
I have a chance to buy a pair of koss pro/4AA phone`s.They have been in a cupboard since 1973 as the chap did not like them,i would
like some info on them please,what are they worth? the sound ,weight Etc.they are in very good condition the cup`s are not leakingthat`s agood sign the chap`s open to offer`s.I would be grateful of any advice at all thank`s.