Unilab 10m FM Output Matching Network - Error in original radio corrected

You may recall from the post here where I first discussed the modifications needed to the PA that I modelled the output matching network as shown below:

With only 40W of RF out I removed one of the trim caps to see if I could learn anything that might explain why. What this revealed was that due to the pin-out of the trim cap it was not connected to the right point in the output network. Instead of the network above we had this:

Actual output network before error spotted

A combination of the trim cap being connected on the wrong side of the LC trap and using ideal parts when real might have been more appropriate mean the output network was matching to perhaps 32ohms, not 50 ohms.

So I connected the trim cap to the correct side of the LC tank. Now I was getting 50W and to be fair that is not a bad result. The 50W was flat across the 10m segment and the second harmonic was 50dB down. The third harmonic was over 60db down and I felt no need to measure it with more precision.

But as I was writing this I realised that an extra 39pF padding the very last trim cap might improve the matching. I tried this but the only benefit was the second harmonic content fell even further.

It appears I have to be satisfied with 50W unless I change the MRF247 to a transistor better suited to this application. If anyone manages to coax more than 50W from a MRF247 at 10m I would dearly like to hear how you achieved this.

Next time I'll publish a circuit for all the PA stage changes I made.

Regards,
Richard VK6TT