NAD: Marshall JMP50

nick · 2011-10-23T18:49:17+00:00

One good Marshall deserves another? I bought a 1973 Marshall JMP50, its labelled as Bass on the back but the first channel is normal and the second has a high frequency cut cleared meant for bass. Will snap some pictures in a bit but firstly some questions if anyone can help: 1.) the 12ax7 sockets are a bit loose, on this amp they appear to have some form of rivet holding it in, can I just drill them out and re-rivet them again? 2.) the bass channel, Im assuming this will just be a few caps to cut higher frequencys, will it be fairly simple to turn it into a normal second channel? 3.) the voltage selector and the impedence selector are both missing the genuine selector cap thingy, tried ebay but these things seem ludicrously expensive, any ideas? 4.) anyone have a marshall volume knob lying around for me? ?

nick

Mine tagged as 'Bass'

Also on the tag

Back, no cover, had the board cut but I still need to get tolex to cover it to match

Front, nothing sexier than a beatup Marshall. Weird glare spot from the camera

Guts shot, mines a late '73 which means its the PCB version.

nick

Images are higher res, the forum downscales them so just use the image link if you want higher res.

1964 JMP Lead and Bass, 50W Head

This amp was in production from 1973 up to 1976. This is a two channel amp, one channel is that of a 1987 Lead amp and the other channel is that of a 1986 Bass amp, making it quite a versatile amp. The 2100 is the combo version of this 1964 head.

Is that not mine?

shaunf

Hey Nick

Thanks for sharing the pics. Your amp is in great condition.

Eish, I don't know much about the later amps (or the earlier ones for that matter) but comparing your board to the layouts I have, I'm pretty sure it's a straightforward 1986 bass circuit. Would need to verify a couple of component values, more specifically that ceramic cap on the bright channel mix resistor, and the red cap in the tone stack, but the fact that it has a shared cathode, has no V2a cathode capacitor, and has 0.1uf phase invertor coupling caps would lead me to this conclusion. Will have a look at the pic again on my pc tomorrow and try to compare some of the resistor values with the layout that matches my amp.

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