In one of the previous videos I described the making of a Tesla Coil with Russian Vacuum tube GU81. This time this Tesla Coil has been modified so that the spark "sings" melody generated by a sound source.  

      Modulator circuit consist of one Power Mosfet and Arduino Microcontroller. The principle of operation is simple: Power tube oscillator, generating high frequency high voltage, is amplitude modulated. Changes in the intensity of the discharge is heard as sound. Thus, if oscillator is modulated by the audio signal, The discharge or plasma flame actc as a speaker. 
Modulation is introduced to the cathode using MOSFET Transistor. In this case it is IRF740, but any Power mosfet can be used. It is only important that it be mounted on a large enough aluminum cooler.

  The source of the audio signal in this case is the Arduino nano microcontroller. For this purpose, a simple codes are presented that generates a certain melody at output 9 of the microcontroller. This signal is now fed to the input of the modulator and next to the Cathode of the Vacuum Tube.
   And at the end, If you decide to make this project, do not forget to watch my video where the construction of GU81 Tesla coil is described in detail, which is the basis for making this "Spark speaker":

     Let me remind you that this circuit is a very dangerous one. The output voltage of this circuit is in Kilo volts and it can seriously injure you or kill you. Try this circuit only if you have enough experience dealing with high voltages. I have no responsibility on any hazards caused by the circuit. Be very careful. This is a humble request.