It is possible to power the anode of an electron tube from electret JFET mic in

At your own risk.


For example the anode of a Nuvistor 7586 electron tube can be connected to the mic in pin of iPad, iPhone or other device witch supplies few volts for powering an electret mic. (Usually it is 1.5V to 3V).


This is because if Pleiades bias is used (typically for this application 1.8MΩ from anode to grid) the the electrons are free from the positive attraction of the cathode and electron type can operate with only 1.2V at the anode. See previous today's posts. The cathode is positive because it has emmited or lost electrons. (Positive) protons are left alone and want the electrons back.


The amplified current will be converted to output voltage by the device's internal power supplying resistor. Just like powering an electret mic capsule with its internal JFET head amplifier.


The cathode of the electron tube is connected to ground.


Heater voltage can be normally supplied to the electron tube by a battery in series with a suitable safety fuse. Underheating should normally be tried. Attention again to safety when using batteries.


Would the protons be left sad and alone? No, electrons will come back through the anode current circuit through the power supply (in our case iPad) and will return through the negative terminal connected to the cathode. See tomorrow's schematic. In fact it is these anode current electron that dance to the amplified music signal. In fact they are the amplified signal.



See also earlier today's euroelectron posts on ultra low voltage anode operation.



An electric bass, hi Z mic, or a low Z mic through a step up transformer can then be connected to grid through a coupling capacitor.


A potential problem is that iPad for example has an internal low cut filter. But it should sound nice anyway.


Vocals for example.