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Geister,
It might help to simplify what's going on in that circuit. It uses what's called a 'back bias' scheme to generate negative voiltages for various other circuits in the chassis. It's used extensively in '30s radios with power trannys and in a lot of early TVs.
First visualize the CT of the HV winding going directly to ground, and the rectifier tube putting out full B+. Now visualize a resistor from the CT to ground. As the rest of the tubes pull current, a voltage is developed across that resistor, and it's negative with respect to ground. The resistor can then be tapped (or a daisy chain of resistors used) to obtain specific negative voltges.
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