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The high voltage on the 5U4 cathode suggests that one of the resistors in the chain may be open.
If you check the resistance from pin 8 of the 5U4 to chassis, it should measure about 6400 ohms. If you check the resistance of the entire divider chain from pin 8 of the 5U4 to the metal can of C147 (located under the chassis under the power transformer), it should measure 7700 ohms. These resistances may vary +/- 20% but if they are considerably higher, then one of the resistors is likely at fault.
Lastly, try measuring from the metal can of C147 to chassis and it should be 1300 ohms. A short circuit to chassis of the C147 can could also lead to a high voltage on pin 8 of the 5U4.
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