The PA module is simple to modify and in fact I found during an internet search a website by a Dutch amateur PA0EHG who had already modified one of these amplifiers and I followed his instructions which worked perfectly.
The PA is coupled with a LPF again from eBay which looks like it's a based on a design by Jim W6PQL the specifications where 2nd order harmonics -35dB and 3rd order -55dB with an insertion loss less than 0.15dB.
When measured with the VNA I found the 3rd order harmonic weren't rejected as much as specified so I expect it might need another coaxial stub filter to drop the 3rd order harmonic a little more.
|70cm eBay LPF filter response.|
To monitor the amplifier I was going to roll my own controller board but again Jim W6PQL has what he calls the ultimate amplifier controller board which at $50 for a kit I thought was a bit of bargain and a lot less hassle than making my own even if half the features of the board aren't being used.
I stuck all this in a rather large Hammond box so its ended up not being a small amplifier but you go with what you have laying around the shack.
I painted the case in acrylic paint and though the result was good looking I don't hold out much hope for it's long term durability.