How Do I Find Out What Circuit My Vintage Marshall Is?

[Tonii]

Ok I have a 1971-73 50 watt JMP NMV head. Old style knobs, 4 input. Window OHM selector. The back has been replaced with just a metal grate I bought it that way. Its made in England and has been modded for American power I assume. I got it for a great price and it sounds killer came with NOS Mullard El34s too. I do not have it here its at my drummers house so yes a pic would be helpful I'm sure. However is there a way to tell via the serial number? Or any other trick, its the only vintage Marshall I own so I'm at as familiar with it as say old Super Reverbs. It sounds ****ing killer instead of buying a "boutique" copy that wil have things I do not want (ie effects loop, master volume, high low gain inputs) and loose its value as soon as I purchase it. Anyways I collect amps and I'm curious what she is besides a kick ass blues rock n roll amp. Thanks.

 

[Blix]

Post some good photos of it here when you can, gut shots and all, and I'll bet you'll know a lot more about it in short time.
Serial number can help for sure, does the serial have a letter? It should be either C, D or E

 

[wyatt]

Does it no longer have a back plate that says Lead or Bass?

It would be easy to tell a Model #1987 Lead from a #1986 Bass from seeing the guts (heck, you can tell by ear...the 1987 is much brighter than the 1986). Guts can even narrow down the year in some cases.

 

[kinmike]

If it has a small headbox it is probably a'71. Marshall started using the larger box for both 100 watters and 50 watters from '72 on.

Mike

 

[Echoplexi]

Sticker on the inside? Usually has a date written down

 

[Tonii]

Thanks for info. I run the bass all the way down but I have always ran Marshalls that way. Yeah the whole back plate is gone where it would say what circuit it is and the sticker on the inside is tough to read. Its at my drummers house I'm going to take some pics. Either way its a fantastic amp early JMPs are very underrated IMO. Is the bass version rarer than the lead version? I may be swapping it for a 71 100 watt Super Lead but I dunno yet.