Battery operated valves

Almost any valve can be operated with even only 4 volts at the anode.


A way is to connect a high Megohm resistor, typically 4MΩ from anode to grid and underheating the heaters.


So conveniently a 3.7V battery for example can supply both the anode and the 6.3V heater circuit.


This method has been found to give healthy anode currents of the order of 100-200μA with just 4-5V at the anode on valves such as:


ECC82
EF86 triode connected
6SN7 or 12SN7 triode connected
EF37A triode connected
EF183 triode connected


Note most of the tubes are varimu and high transconductance.


There is no disadvantge on having low anode currents. Still there are billion billion? of electrons to carry the information from grid to anode.


Perhaps the most impressing operation is with the EF183 and ECC82.


The output impedance of the electron tube or valve is still low since by R=V/I (V is small) and I is not that small). Since there is a healthy anode current there is transconductance too. By disconnecting the anode to grid resistor operation almost completely stops due to electron cutoff and there is distortion to the sound.


There is almost complete absence of secondary electron emission effects at such ridiculously low anode voltage and low temperature of all valve elements, cathode, grids, anode.


Therefore the valve operates at an unheard low noise way which is enhanced or revealed by the purity of voltage supply of a battery.


The anode to grid resistor cancels externally the internal negative bias of the valve due to the electron cloud. (When just connecting a heater voltage to any valve and nothing else a quite high negative grid bias can be observed by measuring with a voltmeter from cathode to grid). The anode to grid electron accelerating resistor is called Rag, Pleiades resistor, or simply RH in honor of Hliana who insisted that valves should not be negatively biased.


An example low noise and great sounding circuit is the Pleiades V6 preamplifier. The Pleiades V4 is a similar unbalanced version with no input or output transformers.


Safety precautions must be exercised when experimenting with battery circuits. For example using a fuse in series with the battery. Noeelry.



References:


On preserving transconductance - Euroelectron blogspot


Operating features of the Audion - Edwin Armstrong


Pleiades V6 or other V series schematics