These were mono blocks with a nominal power output of 80W into 8 Ohms and 120W into 4 ohms. Power supply was a toroidal transformer plus 2 x 10,000uF capacitors.
Some 630s had reliability issues with the 50V capacitors, These should be changed to 63V at service. There is the opportunity to upgrade the PSU by reconfiguring the PSU to use 4 large reservoir capacitors linked by 0R22 (x2) to form a low pass filter.
The original V/VI/VII PCBs can be replaced by the very latest PCBS if some extra tapped hole(s) are created on the heatsink rear surface. A fan drive circuit can be added if need.
The protection is the same as on the 620 and the same comments apply. Speaker protection should always be used as the outputs were originally fuse-less.
Crimson discontinued the 630 in 2003 in favour of the higher power 640. However, the 630 is the more upgradeable.
The original 630 were built with signal ground common to the mains earth (chassis) ground. This made noisy earth loops inevitable. Newer ones had the signal ground floating which made for quiet operation. To increase safety all amplifiers are now built with a signal ground isolated from the mains ground but clamped to within +/- 1.2V by very large rectifier diodes. At service, adding this clamped ground is standard.