Low voltage tubes

In fact it may not be the electron tubes themselves but the way they are used.


For example if a Pleiades bias resistor (usually a resistor form anode to grid typically a few Megohm) is connected, operation is possible at even less than 1.5V anode potemtial. See recent posts on Nuvistor 7586 and EF183 electron tubes at less than 1.5V.


See also the Pleiades V6 schematic:





Experience has shown so far that good candidates are:


Possibly medium μ.


Vari μ.


Multi grid connected as triodes.


High transconductance.


An obvious choose is EF183. The 6SK7, 6K7 should be a second choice for pentodes?


But even a super electrometer electron tube like CV2269 having none of these characteristics can do the trick even at less than 1./V anode potemtial.




Further reading:


The Pleiades Bias - euroelectron


http://www.valvewizard.co.uk/Triodes_at_low_voltages_Blencowe.pdf


http://euroelectron.blogspot.com/2015/10/pleiades-electra-13v-electron-tube-pre.html


Even an open grid can impede electrons:
Operating Features of the Audion - E. H. Armstrong