['LIVEWIRE?']

The heater pins on all B9A base valves are pins 4 & 5. Viewed from underneath, count clockwise from the gap. Nominal heater voltage is 6.3VAC. measured across the pins i.e., between pin 4 & pin 5. The secondary voltages (also AC) are measured across the Transformer windings. In the case of the HT secondary, the voltage can be measured between earth and each end of the winding, although, as the HT DC voltages are reasonable, there is no real need to measure the HT secondary voltage at the transformer. Likewise, if the voltage at the heater pins of each valve is approx. 6.3VAC, there is no need to measure that at the transformer. (Edit; cross-posted with Frank (Nuvistor)