Everyone is blinded by the word "FSK tones" and assume a class C amplifier will work... It won't.
We are broadcasting 8 different discrete tones simultaneously (8-PSK) and that won't simply pass through a class C amplifier without excessive intermodulation products.
You need strict class B, AB1 or A amplifiers. And good ones at that. Simply observe any bands when some hams try to do FT8 with older kilowatt junk amplifiers. They are painting the entire band with junk. They are the one claiming there is no need for an ALC feedback line by the way...
Just read some of the PDF documents available on a search engine (try "8PSK modulation") and keep reading keep reading and again keep reading...
