Can a tube mic pre pre amp be made that operates on 1.3 Volts?

An electrometer tube can be used as shown in an earlier entry.


But can a PCxxx or PFxxx type be used?


Since their heaters operate at 4V, 1.3 Volts may provide the right under heating needed for low anode voltage operation.


Positive grid bias may do the trick as well as output transformer use so that the plate (anode) can be supplied  with 1.3V which is already too low.


The trick is to find a tube that is high gm and vary gm (variable tranconductance) as they have uneven grid spacing. Pentodes are very suitable since when triode connected the 2nd grid (screen grid) acts as an anode and is very close to the cathode to attract electrons.