orange "overdrive" amp head

[hicks81]

i've got this old orange amp head and i dont have any info on it! its got a weird pot on the left hand side that controls something called "F.A.M" or summat like that - it seems to thin or thicken the signal. Also, its got "echo" input and output ports on the right hand side. It seems to have some old U.K. export stickers on the bak, altho they've worn off so i dont know anymore...can anyone help?!

[Anders]

From what I've learned, it's really a crap-shoot to date an Orange. Supposedly, no "Overdrive" amps were made before 1976, but my amp's serial number puts it in the 1974-75 range, AND it has an attached power cord. Maybe it was a prototype? Who knows. I don't really care anymore. I just know that I've got a great, vintage amp that sounds phenominal.