I took a look under the hood and found it to be from 2000. In 2002 Marshall revamped the reissue to include things like an FX-loop and shielded cable runs (wise move). I've read widespread reports about the pre-2002 1987X's "ever-present hum". OK, I know tone purists will say the original 1987 didn't have shielded cable or EL34 grid resistors etc. but for me, these are basic upkeep items that will gaurantee better operation. Another area of concern was the board mounted 68K grid-stopper resistors. I wanted these to be mounted directly on the sockets. Now, although the post-2002 reissue does use shielded cable from the input jacks to the grids, the 68K grid resistors themselves are joined at the input jacks! Saves Marshall two runs of coax...
After looking at the stock schematic, I also decided to restore it to 1969/1970 specs. It seems the 1987 changed a little bit every year but the 69/70 version looked most interesting as it: adds gain, tightens up the sound with more GNFB, makes inputs 1 "true" bright inputs and swapps the monster 0.68uF presence cap for a 0.1uF. The stock 22n plate coupler on the bright input always bugged me as setting up a good mix when channel jumping proved all but impossible. Whatever I did, it just turned into a flubby mess. Schematic files of both the stock and modified amp can be found below.
Here's some gut shots from a real 69' 1987:
http://www.amparchives.com/Amp%20Archiv ... 20SA10859/
Challenges and observations:
1. Getting rid of three pre tube rivets so I could install the terminal strips for the grid-stoppers. These are made of steel and took some patience getting out. I ended up taking a drill to them but they started spinning in the holes rather quickly. Ack! Really frustrating...
2. What to mod and what not to mod? Where do you draw the line? I asked my father if he wanted a Lar/Mar PPIMV so he could chuck the Hot Plate but no go. Elevated heaters? Nah. External bias jacks? Nope. Believe me, I had to work hard at getting him just to accept the coax!
3. Marshall has scraped a copper trace underneath the board so that D4 and D5 anodes don't short. However, the remaining copper trace from point BK5 to D4 was very thin so I bolstered the track with a jumper wire. Be sure to check this trace as the board loader at Marshall may have "gone to town" and removed a bit to much copper.
4. Reuse the stock 0.68uF presence cap and install it in the open slot C6. Frugal or what? Can you imagine the smug look on my face as I made this discovery?
All in all, I'm happy with the way it came out. Noise floor is considerably lower, the sound is gainier but also more focused. I cranked it with a 16Ω Hot Plate into a 1960AX cab loaded with G12M-25 Greenbacks and it sounded killer! Now, I'm not strictly a "brown sound"-connoisseur but I couldn't resist playing "Ain't Talkin' 'Bout Love" as the sound I was hearing hearkened back to that familiar sound. Here are some pics of the amp, starting with a before-and-after shot:
[IMG:925:1024]http://i205.photobucket.com/albums/bb176/jdavidsson/1987X%20Before%20amp%20After.jpg[/img]
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632]http://i205.photobucket.com/albums/bb176/jdavidsson/Pic1_2.jpg[/img][IMG
748]http://i205.photobucket.com/albums/bb176/jdavidsson/Pic2_1.jpg[/img][IMG
768]http://i205.photobucket.com/albums/bb176/jdavidsson/Pic3_1.jpg[/img][IMG
768]http://i205.photobucket.com/albums/bb176/jdavidsson/Pic4_1.jpg[/img][IMG
666]http://i205.photobucket.com/albums/bb176/jdavidsson/Pic5_1.jpg[/img][IMG
741]http://i205.photobucket.com/albums/bb176/jdavidsson/Pic6_1.jpg[/img]
![[IMG:925:1024]http://i205.photobucket.com/albums/bb176/jdavidsson/1987X%20Before%20amp%20After.jpg[/img]](http://s205.photobucket.com/user/jdavidsson/media/1987X%20Before%20amp%20After.jpg.html){kind=link}