Need help

I have an old Polytone amp that I am trying to get more information on and to have a value put on it. I realize that it may be worth nothing to some and alot to others but I can't seem to find out much about the line as it seems to have been replace sometime after 1978 by Polytone's combo bass amps.

Anyway it is a suitcase, solid state, rate at 110W RMS, two channels with a three position tone switch. I am the original owner and I purchased it new around 1975. It is the same amp that I have been playing through on and off in my studio since then. The case is in fair condition for its age with little cosmetic damage. It still works and sounds great for the type of amp it was and time it was made. It has never been serviced so it still contains all original parts. I was told then that this was the first amp that had Ray Brown's endorsement.

I am cleaning up my studio to make room for new equipment and I am considering putting this thing up for auction. However as I cannot come up with any historical information I really have no idea how to go about setting a price.

Honest feedback would be greatly appreciated.