Bridging the Mcintosh 402 amp

I'm going to get another Mc402 2 channel amp as I have one and bridge them to run my Piega C10 Ltds. Before I brought them out of storage, the Piegas were powered with just one of the 402's and it wasn't enough. They are ahungry speaker, so the best economical and pairing option to my Mc2200 tube pre is another 402 but it I'll need to bridge them. I've never done that. What's bridging the 402 entail? Thanks