I do still have everything grounded and bonded after the exercise I went through a few months ago. The only thing I did was replace the KL503HD with the new amp. Nothing is soldered or spliced.
The amp works fine with the Lincoln at 3 watt dead key and 30 watts PEP. I have not tried it any higher than that yet with this radio.
However, it's a different story with the Q5N2 at about 3 watt dead key and 30 watts PEP. I am using the stock mic and tried varying modulation levels. It seems to work well on AM on both low and hi settings and SSB low setting. SSB high is a different story.
This video shows what it sounds like after I have released the PTT button when the amp is on high. It stays like this until I turn the amp off at the 5 second mark. While the voice is (was) crystal clear with the amp on low, when on high it's probably even worse than the KL503HD was. Even more troubling is that now even with the amp off, SSB audio is somewhat crackly.
Now that I am an "expert" solderer (cough), I popped open the Anytone case and had a look-see. There are four IRF520s and I happened to still have some new Vishay ones left from the Digikey purchase I made a few months ago. It only took me about 20 minutes to neatly replace all four. I then re-assembled and re-tested the Anytone with and without the amp. The radio dropped about 5 watts output but the AM voice quality was still fine. SSB without the amp was still crackly and with the amp on high I had the same problem as before.
Carl's said they tested the amp before shipping and it was working properly. I think I have to agree with him because it works fine with the Lincoln. He also said that there should be no problem running the Anytone Q5N2 with this amp. But for me, it just does not work properly with the Anytone on SSB with the same dead key and PEP as the Lincoln and the amp on high. It just really annoys me that I don't know nearly enough to get down to the root cause of the issue between the two of them. Something with the power supply? Or because the radio and amp are both connected to the same 120 amp PSU? I have tried multiple patch cables and configurations but no improvement. I re-checked bonding and grounding and all looks well. SWR is good.
And now I get to figure out what testing the Anytone with the Carl Built did to the SSB audio quality. I assume it had something to do with the feedback generated when the amp was on high and did not unlatch.
This is definitely a mix of frustrating/fascinating.