How different is a 50w MV JMP from a 50w JCM800 with horizontal inputs?

[Cossack]

My understanding--based on hearsay and internet lore--is that the master volume JMP and the horizontal input JCM800 represent the first and last renditions of the same design, barring reissues. Would one expect these to have roughly the same basic sound other than the age and varying tolerances in components? Or is there an inherent difference? I'm aware that there will be a difference in even the same design from the same year because of variations in the components. But is there a significant difference in this design as it evolved from the '70s to the mid/late '80s?

 

[RCM 800]

I only have clones but Im interested in the topic.

 

[Purgasound]

I've got an '83 and two '87 2204's. They're the same. If you were in the U.S.A. then '80 to '84 would have 6550's and '84-'89 would have EL34's.

JMP's do get a little different, there were lower voltages on the B+ in the older ones. The older transformers are also designed around 110 for the US and not 120. They fixed that by the time the JCM800's rolled around. There's also the non-cascaded JMP 2204 which was '76 and early '77.

So yeah there's a couple variants but more just on the JMP side of things.

The lore is based around some people thinking things changed when they went from vertical to horizontal inputs, the circuit didn't change they just streamlined the manufacturing process by PCB mounting the pots and jacks. The 100W changed some filtering but the 50W stayed the same. The horizontal input models are actually way easier to work on.

 

[colchar]

I have heard the same thing (I maybe even read it here).

I used to have an '83 JCM800 2203 which had the vertical inputs. I bought it from a friend, and he had previously checked it out against some amps owned by another mutual friend. That guy has at least one, and most often two, JMPs from every year they were manufactured. From what the two of them said, the JCM800 was the exact same as the late JMPs they had tested it against. And we are in Canada so all of the amps they compared had the proper tubes, unlike the US models.

I never should have sold that amp.