I don't know anything about them but there appears to be more than one generation of them, and I'm not sure if they are all valued the same. One was recently on eBay advertised as "late 60s" then the guy said "someone says it is actually early 70s" and it sold for around 450. Then there is one on NJ CL the guy was asking 450 but now it's down to 280 and still hasn't sold. That one looked similar but different from the first eBay one. (And now there is another on eBay). Some of the knobs/controls might be different, and maybe the writing. But they all look the same at first glance. Not sure how they sound or how they differ, if at all