Very disturbing!
The first explanation that occurs to me is that you may have installed the 4-pin tubes or sockets rotated 180 degrees.
I just now checked page 32 of the manual, and sure enough there is no warning or caution about orienting the socket correctly. We'll have to fix that! Looking at the socket, you will see that two of the holes are slightly larger, these are pins 1 and 4. (They are larger because they carry the filament current, which is much greater than the other connections.) They should be the two holes closes to the hum-balance pot. On page 46 of the manual you can see where the filament power is wired to those pins, and on page 63 the hum pot is connected through the 22 ohm cement resistors. When the tube is inserted into the socket, the larger (fatter) pins should go into those holes. Occasionally someone will force the tube into the socket incorrectly - it is possible, though fairly difficult. I suppose this is one of the reasons that later tubes have a more unequivocal orientation!
If you have reversed the socket, you'll have to fix that. You'll want some solder-sucking copper braid to get the wires off the pins; other than that it should be easy. If you've inserted the tubes incorrectly, the small socket pin connectors may be stretched out - make sure you have secure connections before testing again. If the socket is too badly damaged to provide reliable connections, Eileen can fix you up with replacements.
If neither of these is the problem, then we'll have to re-visit the situation, and perhaps ask for a few more measurements.
