Micro Build Report: Hardrock HF-50 HF Amplifier

Estimated reading time: 3 minutes

The HobbyPCB Hardrock HF-50 Amplifier is the perfect companion for a QRP radio such as the Elecraft KX2 or a Yaesu FT-817ND. It can be directly driven from your QRP radio and generates > 50W of power from 160 m up to 10 m. This has been verified experimentally (see table below). Fun fact: I’ve taken my Hardrock HF-50 up with me on summit in order to operate QRO-portable during the European SOTA Activity Day 2021.

The Hardrock HF-50’s assembly instructions are easy to understand and the construction is a real joy. If you don’t want to wind your toroids yourself, there’s an US-based ham offering to do toroid-winding as a service. He wound all the toroids for the HF-50 + ATU to order and I’m really happy with the results. Also the next time I’ll wind them myself, because winding your own toroids gives you a more thorough DIY-feel 😉 .

There exists an easy to use adapter which allows automatic band-switching of the HF amplifier. Furthermore there is an possibility for upgrading your HF-50 with an internal ATU (I’ve done this and a picture can be seen below).

Now let’s move on to measuring the Hardrock HF-50’s RF output power: The test setup consists of a Yaesu FT-817ND, a Hardrock HF-50 HF amplifier, a Maas SPA-8350 13.8 VDC stabilised power supply, a Diamond SX-100 SWR & Power Bridge as well as AV-DL200M dummy load.

As can be seen from the table below the generated RF output power exceeds 50W across all bands thereby supporting the claim made by HobbyPCB.

This is a real fun kit to build, it works reliably and allows you to dual-use your QRP radio both for SOTA as well as at your home QTH. I highly recommend it 😉