[mikethedruid]

From what I can see in the schematic, caps 73 & 74 go from each plate of the rectifier tube to ground. They are isolated from the mains by the power transformer and so cannot short out across the mains. I would use regular 600 or 1000 V poly caps for them. I believe they chose to use the RL circuit with R78 and R79 on the primary (mains) side of the transformer for just that reason, and to also provide filtering there. It is the only explanation I can think of for their being there.