DF9IC 23cm PA progress

My first DF9IC 23cm 250W PA board has been running for a month and it is working well, although I think the output capacitor positions still need a little optimisation. I am using the 9160s from utsource.net and the professional PCBs direct from Henning.

At about 8W drive, my Bird 4410A with a 1GHz slug reports 230W out for 7W in.   I think the 4410A 1kW slug reads 9% low at 1296MHz, so that is about 250W in reality.  That is using 30V and about 22A.

The 2p2 caps on the output lines are 12,76mm and 11,55mm from the FET body.  I will build two more PAs and try to tune those more carefully, but for now, this one is working fine.


I soldered the PCBs to the heatspreader using the same 138C low-temperature solder as I used to fix the FETs.


I am using a water-cooling plate for the PAs.  The heatspreader is a copper block 100mm x 71mm x 12.7mm.  After 3 minutes of full power, the heat spreader temperature close to the FETs is 23.5C.  I think that is cool enough!  It works really well on JT modes and CW at full power.

I find that running 1.5A standing current for each FET gives best IMD performance on SSB.

Looking at the two-tone spectrum, with 165W actual output, taking 12.4A at 30V, the output spectrum from a pair of pure tones 1.2kHz apart looks like this:


At higher power, the IMDs start to rise, with the 3rd order -20dB at about 220W actual power, and the 9th and higher start to come up much above that.  With speech it looks nice and clean, very straight sides to the spectrum at 150W and still OK at 200.

Next stage is to combine two PAs.

Henning’s website is at www.df9ic.de

5 thoughts on “DF9IC 23cm PA progress”

  1. Nice work!
    Do you know the details of the enamel wire inductors – thickness, number of turns, spacing between turns?
    I haven’t been able to find any details yet.

  2. Hello, I am from Spain (ea7ig) and I am interested in a professional termination pcb of the PA 23CM 2X MRFE6s9160 from DF9IC, as I can contact me to request a unit of this PCB

    I have mounted one, I have tried with different PCBs but I do not achieve much power, gacias I expect your answer.

    1. I have made 2 of these PAs. First one made 260W with 8W drive. Second made 270W with 7W drive. I used 30V DC and the current was 22A at 270W.
      The input tuning capacitors I used are not those specified by Henning. They have a higher Q factor. The input tuning is very sensitive.

      Phil G3TCU found it was best to adjust the position of the output capacitors using a jig to allow the capacitors to be moved. I used devices from utsource, purchased in April 2016.

      I used the PCBs supplied by Henning for both of my PAs. Phil G3TCU also used Henning’s PCBs.

  3. Just built the same amplifier with pretty much identical results to yours. P1dB seems to be about 230 watts for 8 watts drive
    P sat seems to be about 300w
    not very efficient as it draws 21 amps at 28 volts but I guess I just need a big cooling fan

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