Mars 300B Kit

  • Post category:Stereo
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Our stereo single ended 300B kit is now available.


  • to supply a 300B kit for experienced electronics enthusiasts
  • voltages are chosen so that the 300B’s are not stressed unduly
  • voltage across 300B is 350V
  • the load impedance is 3000 ohms
  • the bias voltage is -74V and the idle current 60mA
  • with these conditions second harmonic distortion would be 26dB and third harmonic distortion 38 dB
  • the circuit is straight forward 6SN7GT driver and 5U4 rectifier
  • the CLC power supply (Capacitor/choke/capacitor) is designed for optimal stability
  • two center tapped 5V secondaries for the 300B filaments supplied on the power transformer

This is how Duncan’s PSUD2 models the power supply:

As you can see above,  R1 can be tweaked to drop B+ and R2 can be tweaked to get 280V after R2.

C2 is a series capacitor bank with a max voltage of 700V and total capacitance of 340uF. C1 has been chosen to work with the 5U4 and the choke for a fast and stable voltage.

We have chosen a symmetrical layout for weight balance and channel separation. Here you can see the casing with upgraded C-core output transformers on top

Filter capacitors goes underneath.

If you are interested in building this amplifier, contact us for pricing. We also offer workshops where you can build this amplifier yourself, with expert guidance from us.

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