This is the home page of the A600 – my 2x MRF300 600W amplifier project for HF/6m, as initially described in this article. Here I will post the latest developments.

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General features & specifications

  • 1.8-54MHz coverage, 600W output, 20+dB gain
  • uses a pair of low-cost MRF300 LDMOS transistors. These are proper RF power transistors housed in common TO-247 packages.
  • onboard sensors for supply voltage, supply current, heatsink temperature, output power & reflected power. These are available via the Sensor Port and can be read directly by most microcontrollers, including most Arduino boards.
  • connectors for an external bank of low-pass filters, so they are inserted between the amplifier and the output coupler

A600 version 1.2

  • returned to original component references, as used on v1.0 PCB
  • replaced T2 transformer with two separate coils (L2 & L3), 3 turns on ferrite cores. This improves efficiency and P1dB below 14MHz, but 1.8MHz matching is slightly worse.
  • changed input network (C43, T1, R6 , R7) for better overall gain (around 22dB now) and better matching on 50Mhz. Input SWR is now below 1.5:1 on all bands.
  • added 2k4 resistor in series with the bias compensation thermistor, as it was overcompensating. Quick test, heating the heatsink from 25 to 45C changed the idle current with less than 2%.
  • fixed a few small mistakes in the schematic and rewired the Sensor Port to the correct pinout.