05-02-2022, 01:25 PM
The hum balance pot has no effect on the actual heater voltage applied the various tubes. It only affects the relative AC voltage as measured to chassis ground seen by the output tube filaments.
Looking at the schematic, it appears that there are more heaters fed by the Fil 2 winding than the Fil 1 winding. This would place a greater load on Fil 2, resulting in slightly lower heater voltage to those tubes. The tubes you mentioned are fed from Fil 2 and would consequently read a lower heater voltage.
This appears to be normal and inherent in the design. I would not be overly concerned, as 5.8 VAC on the heaters is still within the + and - 10% tolerance specified by the tube manufacturers.
Looking at the schematic, it appears that there are more heaters fed by the Fil 2 winding than the Fil 1 winding. This would place a greater load on Fil 2, resulting in slightly lower heater voltage to those tubes. The tubes you mentioned are fed from Fil 2 and would consequently read a lower heater voltage.
This appears to be normal and inherent in the design. I would not be overly concerned, as 5.8 VAC on the heaters is still within the + and - 10% tolerance specified by the tube manufacturers.
