Mcintosh MC250 ( Does this look like some of the caps have been replaced)??

S/N: 10L01~91L43 (7,883 UNITS) from March 1967 to May 1979

So 59L31 would put it a little past midway in its production run. Maybe 1974ish? I don't know that there is an exact science beyond that. 

Roger Russel says 1967 - 1979...wow..quite a run....
so a call to factory probably in order...

call mac
or Audio classics

Thanks all.

Any other info on where I can narrow down the build date by serial number??

I had a 250
the blue cap topside is definitely not stock, my guess is the GE is stock
the interior purple caps are also new.
the amp was designed to replace the venerable 240, so the sonics for early SS are actually pretty good - sins of omission....I used mine while rebuilding my 240
accounted itself well driving 3 ohm Apogee Stage.
have fun
enjoy the music
Jim

That big, blue Phillips should have been either a GE or Mallory, in a can. So- those and the 470uF caps: yep, new. The multi-section, GE, can cap, may be original. The white, film caps look original. The power output boards(mounted under the output heatsinks) have one 470uF, 4V, electrolytic each(C11 and 12). The ones in your pics are original. You might want to replace those(6.3V caps are fine).

The blue 9300uF and the two 470uF caps look like replacements.