I would not use the 500 without puresignal wrapped around it..maybe the same for the 600. Im sure you've looked at the transistor spec sheets. -24db at 100 watts for the 2879 leaves a lot to be desired. The mrf 150s in the ALS 600 aren't that impressive either at -32 db. If you buy the 500 new will it come with Toshiba transistors?
Ameritron doesn't give IMD specs for either amplifier in their respective manuals. They do with their tube amps. Most of them are "-35 db or better".
I'm not sold on the solid state stuff yet.
I know this post is a little old, BUT..........
I have one of these ALS-500M amplifiers to use in mobile use for all bands.
Manufacture date sticker inside is 02/2022 .......
Quality control sucks. It would not key when everything was connected. I had to troubleshoot the amplifier using Ameritron's schematics. Finally traced the issue to faulty assembly work on the bias PCB ...... Working just fine now.
It came with, believe it or not, PP100 transistors ........ I was blown away when I saw these transistors in this amplifier.
Upgraded the power wiring, and installing 4 brand new Original Toshiba 2SC2879 transistors. These are from my personal stock.
It should perform just fine for mobile HF operations. I am just looking for 350 +/- watts or so for mobile use.