This is interesting, below from posted description. Couldn't get the URL to embed. Maybe someone more tech savvy can post URL
Serial A802, was made in late 1976 two amps before Keith Richard's legendary A804! This was originally a 100/60w amp, then factory upgraded to Simul-class in the mid eighties (transformer code is 1985). This upgrade work was confirmed to be factory performed when the amp was sent back to Mesa for a full service and cap job in April 2018. Surprisingly enough I was told this was not the only Mark I to be upgraded to Simul-class, but I have certainly never seen another.
Serial A802, was made in late 1976 two amps before Keith Richard's legendary A804! This was originally a 100/60w amp, then factory upgraded to Simul-class in the mid eighties (transformer code is 1985). This upgrade work was confirmed to be factory performed when the amp was sent back to Mesa for a full service and cap job in April 2018. Surprisingly enough I was told this was not the only Mark I to be upgraded to Simul-class, but I have certainly never seen another.