This is my amp. Still figuring out how to post three pics. Where to put the urls? I bought it in the mid 80's. I researched the serial number and it indicates it is a 1978 model. 01777K. Is this considered a vintage Marshall Amp? It has no mods. The vent is on the back not the top. Is this then a Marshall JMP Master Model 50w #2204? It does say JMP on the front but I find Marshall history confusing. It has both a master volume and pre-amp knob. I read something about Marshall cascading the pre-amp to give extra pre-amp saturation in order to produce saturated tone at any volume. I plugged in two cables at the same time into both inputs of the amp and only one produced sound. I think this means it has the cascaded circuit. If both produced sound then it would be a non-cascading circuit. What do you guys think? What would it be worth on the market today?