Is a portable Single Ended class A electron tube power amplifier possible?

This is a next part on Pleiades electron tube power amplifiers.


Not really portable since the output transformers might still be heavy.


It may be possible with 5x 9V Bulgin battery holders secured in the chassis. And 5 Bulgin 1.2V AA battery holders. Rechargeable batteries may be used. In this way very pure 47V and 6.3V are possible.


If EF183 electron tubes are used...


It may be possible to draw 20mA from the cathode. Do cathodes sound better when near saturated by taking most of the elecyrins they can supply? This may be a similar idea to underheating the cathodes (see Pleiades V series pre preamplifiers). But this time the cathodes are normally heated and the cathode current is increased to its limits for the particular 6.3V heating.


The very high anode to grid resistor trick may prove useful for increasing the current at low voltage conditions.


The EF183 electron tube may have an internal resistance of 2.5KΩ? at Va=47V, Ia=20mA.


50V x 0.020A gives 1 Watt anode desipation. This gives a theoretical 500mW output? It should sound loud enough because of the way electron tubes produce harmonics, see Russel O. Hamm reference.


So it may be possible to have a great sounding 2x 500mW electron tube power amplifier operating in class A (electrons flowing all the time).


If input sensitivity is not enough an input transformer may be added.


Cathode may be tried to be connected to ground. So a very high Megohm impedance resistor could be used for bias either from grid to ground or anode to ground. If it is not possible then the schematic of the Neumann U47 microphone could be referred too again for inspiration.


The Pleiades power amplifier may use only one electron tube per channel.


One or 2 transformers. 1 resistor, 1 capacitor. And just a few batteries.


An operating battery time of 7 hours may be possible.


The schematic should be very similar or almost identical to the Pleiades V6 pre pre amplifier.


References:


Neumann U47 schematic


Pleiades V6 schematic


On preserving the transconductance of electron tubes at an anode potential as low as 3 volts - euroelectron


Tubes vs Transistors, Is there an Audible Differnece? - Russel O. Hamm - Journal of the Audio Engineering Society