Just about any power transistor can be used in  this megaphone.Its suitable for boats,playing fields etc.the transistors Q1  & Q2 are the HEP-230 type which are easily available in the market.The transistors are parallely connected to handle the required power and speaker matching.The microphone is a carbon type like that used in telephone hand sets.If  a regular carbon mike is used the push-to-talk (PTT) switch can be connected in place of S1 to provide PTT operation.There will be no warm up or “capacitor charge time.

Circuit diagram with Parts list.



  • The circuit can be powered from a 12V battery or 12V DC power supply.
  •  The POT R1 can be adjusted to obtain maximum volume with minimum distortion.
  • It will be always better to mount the transistors on heat sink.


  1. what is the maximum output power of this circuit? What type of a mic should be used?

    • Seetharaman

      Hi Mic should be carbon type and with the shown germanium transistors the power output will be around 2 to 2.5 watts.

    • Seetharaman

      Hi Rex HEP 230 is a PNP power transistor similar to AD149 or 2SB337. As the transistor is pnp collector should get connected to negative and emitter to positive. Mic should be carbon type only. To start with keep R1 at maximum value and by talking into mic slowly adjust the pot till god quality (un distorted)sound is heard with good volume. by adjusting R1 further will increase the current consumption and reduce the volume also. Never try with a car battery you may blow the transistors instantly in to smoke.

  2. Apart from Carbon mic, Can i use Electret mic, dynamic mic, or Condenser mic.

  3. what type of mic will be the best to this circuit??

  4. If R1 (potensio) turn to zero ohm, the base Q1 and Q2 are + 12V. Speaker not burn ???

  5. scientist jones

    it sick outa proportion member mi tell yuh dat!!