Just finished a project of converting my old 4 sweep tube amp to 4cx250. I f
the amp uses a doubler type power supply forget it. Might as well build from
scratch. Bridge type power supplies can be converted to doublers that will
give about 1600 VDC. At this voltage power out of the 4cx250 will be about
the same as 4 sweep tubes. Im getting about 800 watts PEP. Dont even think
about running 2 4cx250s, OF course you could but the rest of the amp parts
will never handle it and again you might as well build from scratch.