Electron tube amplifiers operating with 1.2V at plate (ie anode)

By looking at past Pleiades notebook entries (written before or after a euroelectron post)...


In mind was searching for comments such as... "the sound quality reminds of the easiness, detail and fullness of When I Fall in Love - Nat King Cole".


One such entry is date time code 18080417. (There should be the corresponding post near 4/8/2018).


It is Pleiades V6 mic booster amp with Nuvistor 7586 operated with 1.2V at plate and MD211 mic used with Pleiades (130Ω, 40mH) passive low slope high pass filter.


Also V1 mic booster amp with electrometer tube operating at less than 1.2V with MD441 and Freed input transformer gradual high pass characteristic. Very nice sound comment too.


In all these experiments very low potentials and currents are involved. Typically Va=1.2V, Ia=2 to 10μA.


Could it be that there is something very special about low anode voltage and low anode current?


Low anode current ie 10μA sounds great with a higher plate potential such as 9V on EF183, grid at space potential.


But low anode current, low anode voltage such as 1.2V anode voltage seems to sound even better.


Usually 1.9MΩ is used from anode to grid in these cases to make the control grid less negative with respect to cathode. (Pull up bias for the default negative grid space charge potential due to emitted electrons from cathode).


More experiments needed.