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R84 is a soft connection from the circuit common to the chassis. If you measure with a high impedance meter (like most modern meters), the chassis will behave more or less as if it is connected directly to ground in terms of measured voltage. So relative to the B+, you might see something like -250 VDC on the chassis. I would check the resistance from the chassis to the circuit common and see if you get the expected 470K from R84. If the resistance is lower, there is a short somewhere (solder blob, some wire touching, etc.).
Even if you checked those high megohm resistors before, as Tom C points out, they may have suddenly died in recent days. It's actually fairly rare to find those particular resistors still good in these electrostatic sets.
Also, check the voltages on the vertical oscillator and output tubes to see if they match the Sams chart reasonably well. Do you have a scope? If so, check to make sure that both triodes of the vertical output have a nice output waveform on the plates (huge sawtooth at 60 Hz, with opposite phases).
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