Circuit differences between early and late stock Marantz 9..

Archived from groups: rec.audio.high-end (More info?)

After looking at the under-the-chassis images posted in ebay and
elsewhere it appears that the earlier M9s (e.g. serial # less than
1200) have a different circuit from the later ones. The schematics one
can find from the web seem to correspond to the later ones only (e.g.
with the 2V neon light at the 6DJ8 phase splitter).
Would anyone know how many different circuits had been used in the
production history of the M9? Which version(s) are considered to be
better? Are there other major component differences (transformer etc.)
between the early and late productions?
Also would appreciate any pointer to an earlier schematics of the amp.
Can one tell exactly which circuit is inside by the serial number?
Best and TIA