I highly disagree on both use of solid state rectifiers, and the point of when tube starts conducting. I find that it averages, with a known good rectifier, that it starts producing a low voltage at about 35 volts input on variac.
By 50 volts, you are surging at over 140 volts dc. Mind you, that's surge. As set warms up, this voltage quickly drops. By 85 volats on variac, you are putting out over 200-250 volts dc. At full line voltage, you should get the full dc rated voltage. Note: Back then, the full rated voltage was 117 voolts AC. At least here, in Fl. today's line voltage averages around 124 volts ac.
Further notes, According to John Foltsom to get the correct dc voltages, negative lead of your meter must be connected to chassis.Not to the negative supply lead. RCA was putting in a negative bias supply on this series of chassis. That is why you find the positive terminal of one filter connected to chassis.
Further warning: Remove the black caps going from both sides of line to chassis, as well. You can put in new ones if you wish. I believe the original value on these earlier sets was .01 600volts dc. I personally leave that, and the sometimes installed 270K resistor out of circuit. These two caps were line filters intended to filter out car engine generator noise, medical devices, etc. I find that leaving these two caps out has had NO detrimental affect on the operation of the set. In Fact, with out them, the set is electrically slightly safer on the chassis, making it less of a shock hazzard. Mind you, I'm not saying NO Shock hazzard. I'm saying less.
Please take every precaution on measuring voltages, and handling this set. I'd reccommend one hand behind your back, use clip leads for positive connection, and, have your shoes, and socks on. A rubber matt can also add further protection.
Bill Cahill