Is there no current, voltage starvation when a pull up grid bias is used?

In an ordinary further negatively biased circuit suitable for operation of an electron tube at 300V, the electron tube may not sound nice or may not sound at all at say 3V plate potential.


But if pull up or Pleiades bias is used to increase the already negative grid bias by electron velocity emission [Atkins] the electron tube will operate in a normal way, at 3V, at the suitable bias for 3V. For example the Pleiades V6. With a few Megohm resitor from plate to grid the grid bias becomes from -700mV to a suitable -70mV for 4 volt plate electric potential.





Pleiades V6 schematic, a 7586 Nuvistor electron tube can also be used as well as others, 12AU7, 6SK7 etc


Electrons arriving at the anode will not aproach speed of light, will not so abruptly collide with plate to produce blue light or even soft X-Rays but who cares.


The operation can be more quiet, [Llewellyn].


And a fabulous example of a relatively low plate potential is the "mighty sports car" Neumann U47 microphone with lower cathode temperature and a plate voltage of the order of 40V. Strangers in the Night does sound good.


And a 9V plate supply electric guitar pedal operating with a 12AX7 with pull up bias resistor can be read on the net to be used by such artists as Dave Gilmour, Pink Floyd. The Tube Driver Chandler pedal, patent US5022305.



An electron tube operating with a low tension rail will possibly achieve the tube sound [Hamm] so important for record production including mastering with much fewer amplifying stages needed.


Of source pull up bias should not be overdone with a too low + to grid or anode to grid resistor or the electron tube operating point will shift further from the linear part of the transfer characteristic curve? Is this the reason why? See yesterday's post.


References, further reading:


A study of noise in vacuum tubes and attached circuits - F. B. Llewellyn - proc IRE Feb 1930 - vol 18 no 2


BBC report on Neumann U47 microphone


Low Plate-Potential Tubes - C. E. Atkins - Radio & Television News - Jan 1957


Triodes at Low Voltages, linear amplifiers under starved conditions - Merlin Blencowe


Tubes vs transistors (vs operational amplifiers), is there an audible difference? - Russel 9. Hamm - JAES


http://www.effectrode.com/faqs/do-the-tubes-operate-at-true-amplifer-plate-voltages/


The Pleiades Bias - euroelectron