A cupboard opened a little by chance.
Then while it was fully opened a small pocket size opaque plastic box fell on the floor.
It can just fit an AA battery holder in series with a fuse holder (for safety).
2 1/4 in mono female chassis sockets.
And just a Nuvistor 2DV4 or even a PC92 electron tube. Or soldering the leads (sleeve insulated) of a CV2269 electrometer electron tube, (see Pleiades V1 microphone head amplifier).
Will it work? Just 1.2V on both heater and plate. The electron tube will be underheated. This means less cathode grid (emission) current.
Balanced in or out can be with 1/4in to XLR impedance converting transformers. For example Canford red Neutrik 1/4 jack with internal transformer etc.
After the fuse, battery + connected to plate (anode) through the external output transformer or load resistor. So plate is connected to signal pin of the 1/4in female output socket.
Battery - connected to cathode, one side of the heater and ground of the 1/4in connectors.
After the fuse, battery + connected to a switch and then to the other side of the heater.
Signal in from the input 1/4in female socket connected to grid through a small coupling capacitor to isolate the grid bias.
A pull up resistor from anode to grid provides bias, Pleiades bias.
The box is opaque so everything would be transparently seen from all sides.
There won't be hum as it is battery powered. But there would be electromagnetically induced noise if it is brought close to e/m radiation emitting equipment.
It would be like Pleiades V6 but with the transformers as external option. An instrument can be directly plugged. The load resitor can be the input resistor of the following amplifier. Normally a smaller Rag bias resistor would be required to bring the grid as far up below 0 volts or cathode potential for class A operation (electrons flowing all the time).
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