MV Triple Firing Board (HGC Part P561T)
The Hill Graham Controls MV Triple Firing Board (original part number P561T) provides block-pulse firing for one half of a 3-phase, fully controlled SCR bridge. They are used in pairs to provide 6-pulse firing control. This board was later upgraded, but care should be taken when mixing and matching the newer model with the earlier version: the terminations are slightly different, and boards should not be mixed in individual SCRs. Use the correct part wherever possible.