How low can the anode voltage get?

A way to experiment with may be using the Pleiades V6 circuit:






Connecting a capacitor between anode supply and ground. Then disconnecting the supply only to the anode while the amplifier is operating. The capacitor will slowly discharge allowing an infinite range of small voltage to tried. Monitoring of voltage can be with a suitable voltmeter across the capacitor.


Adjustment to the Pleiades bias (anode bias) resistor may be needed as well as cathode temperature optimization by varying the heater voltage.


An important reason why the Pleiadss V6 is so low noise possibly comes from low temperature on all electrodes. So there is minimum photo emission, thermo emission, the low accelerating fields by low voltage ensure minimum secondary emission. The not high negative bias does not attract positive ions around the grid and space charge. See recent euroelectron posts with references on fluctuation noise in vacuum electron tubes.