HF Amplifier 50W 160M-15M

My low cost  amplifier has been modified yet again.  I added a different filter board so that the amplifier will work from 160M through 15M.  The previous version had a home brew filter board covering 80M, 40M, 30M, and 20M.  Instead of re-doing the filter board to include more bands, I decided to go with the following filter board from HF Projects:

HF Projects – Low Pass Filter

Below is an image of the filter board (right-side) and the Arduino amplifier controller (left-side):

50W Amplifier

50W Amplifier

I found that the amplifier started to loose its efficiency above 21Mhz. I also had some issues with the COR/PTT board causing self oscillation; I went with a simpler solution.

Here is the schematic of the Arduino amp controller. Note that this is work in progress:

amp Controller Updated

The latest version of the Arduino amplifier controller  is found here:



PTT/COR Schematic Diagram

PTT/COR Schematic

PTT/COR Schematic



2 Responses to “HF Amplifier 50W 160M-15M”

  1. Al, CX8AT Says:

    Hi Jim,

    Nice amplifier.
    I have 4 questions about it
    Would you please tell me the data about the toroids in the output transformer (material, form type, etc)?
    What about the bias settings? How many mA per fet?
    What is the input power for exciting this amplifier? 1W maximum?
    and the last one is: what are those resistors that come out from the primary of the transformer that are not connected to anything yet? Are R15 and R16?

    Thank you in advance

  2. Chris Says:

    Hi Al,

    The output transformer T2 is a Binocular core type 43 (RF600 Type 43 from Communication Concepts). 1 turn center tapped primary and 4 Turn secondary.

    I adjusted the bias to about 12ma per transistor, which comes out to about 3.6V measured at R1.

    It can be driven to full power at about 2.5W in but less on the lower bands.

    The resistors that you see are R15 and R15 and get attached to C13 and C14 on the input proto-board.

    This amplifier is based on WA2EUJ QST article. I understand that he has a bare amplifier board available (www.hobbypcb.com).

    It’s been a reliable amplifier despite it’s ugly construction. It was really proof of concept for me.