Marantz 1200 vs Marantz 1200b

I can't  seem to find any information on the Internet the explains the difference(s) between the Marantz 1200 and 1200b. Face plates and rear panels look the same, but there was a $105 list price increase.
Does anyone have any credible information? Parts upgrade, circuit redesigns?
[PDF]Marantz-1200-Service-Manual-1 - Vintage Hifi
[PDF]Marantz-1200-Service-Manual-2 - Vintage Hifi

The service manual contains all the info

rumor has it that:
The 1200 has the same driverboard as the 250 mk1
The 1200b has the same driverboard as the 250 mk2