is there a stereo blue book for value of old gear

Orion Blue Book issued each year. Used versions sometimes available here.

I believe it's called the Orion Audio Blue Book. Most Hi End audio shops should have a copy. You could probably buy one from a technical book shop or go to www.orionbluebook.com.

It really doesn't reflect true market values. It's primarily a tool for dealers.

Although I have not seen one in recent years, I always found Orion to under value equipment. My suspicion was that it's real purpose was to justify dealer's low ball quotes for trade ins.

You can also subscribe to the Audiogon blue book. Not affiliated with Audiogon..... totally ignorant.... not responsible when it doesn't work, etc......