This is the home page of the A600 – my 2x MRF300 600W linear 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

  • 1.8-72MHz 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, drive 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


Update – 23rd September 2022

  • After many delays related to parts availability and manufacturing challenges, the A600 kit is again available. Version v2.3 brings small changes, most significant being current sensor output; performance, layout remains the same.
  • Once again all kits (A600, F1500, B1500) can be ordered from the Shop area and will be shipping from stock, typically next working day.
  • Component costs have unfortunately affected overall prices, which had to go up.

Update – 3rd March 2021

  • F600 LPF Unit kit has been replaced by the new F1500 LPF Unit, offering higher power handing (1500W PEP) in a very similar package
  • All kits (A600, F1500, B1500) are shipping from stock, typically next working day. Check out the Shop area.
  • After the recent changes cause by the UK leaving the European Union, all deliveries outside the UK will have to include a customs declaration with attached commercial invoice. Also, prices are now expressed in GBP instead of USD, but you will still be able to pay in any currency via Paypal. The currency conversion will be automatic.

Update – 22nd March 2020

  • The B1500 RF amplifier Backpanel Unit is now available. It features RX/TX switching, 2-port antenna switching, transceiver interfacing and has an onboard 12V DC-DC converter.

Update – 22nd February 2020

  • After a long delay related to challenges with China logistics, a new revised version of the A600 Amplifier Unit is back in stock. v2.1 brings improvements in ruggedness and is available to order here.
  • The Backpanel Unit is almost ready as well and will be announced soon.
A600 v2.1 schematic

Update – 24th December 2019

  • LPF board kits are on the way and will ship after 6th of January; two thirds of the first batch are already gone. Can be ordered here.
  • A new Backpanel unit is in the works. It will handle RX/TX switching, transceiver interfacing and includes a 12V/3A DC-DC converter and a 2-port antenna switch. Expected in the 2nd half of January.
  • This has pushed the Control Unit further back. I know this unit is expected by many of you, but it’s worth the wait as it will support all the features added by the Backpanel Unit.

Update – 7th December 2019

  • A600 v2.0 kits now available, includes multiple improvements. More details here, order the new kit here.
  • LPF board sent to production, kits will be available soon.
A600 v2.0 schematic

Update – 2nd December 2019

  • Published assembly instructions for the v1.2 kit, see above.
  • LPF board is still under testing; the prototype achieves the desired attenuation but I’d like to improve insertion loss on a few bands before I release the design and make the kit available.

Update – 20th November 2019

  • Assuming no further issues, the next batch of A600 amplifiers will be ready to ship in the first week of December. Includes some tweaks.
  • I started working on a compatible Low-Pass Filter board. Should be ready early December.
  • Still on track with the Control Unit for mid December announcement. The hardware is almost done but sorting out the software takes time.

Update – 15th November 2019

A600 v1.2 kit was available to order here. Sold out in less than 8 hours so new batch on the way, hopefully by the end of November.

Updates – 14th November 2019

  • This project has been awarded the 2nd prize in the NXP Homebrew RF Design Challenge 2019. Really appreciate the opportunity and congratulations to veteran Jim WA2EUJ and the Stanford University team led by Weston Braun for their results.
  • Kits are almost ready but some parts are delayed due to courier issues. I plan to start taking orders in the following days and ship out after 20th of November.
  • An advanced monitor, control and protection unit is in the works, featuring a large LCD touchscreen. ETA mid December 2019.

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 24dB 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.
A600 v1.2 schematic
A600 v1.2 gain