Earth's solid state amps were copies of Peavey amps, especially 130 series gear.
The Tube stuff were copies of Fenders.
The biggest problems with the Earth amps (solid state ones) was they were made relatively well, but the output transistors they used were often under spec.
There was a story about Peavey getting wind of what ESR was doing, and having an ESR tech get shipped out to Mississippi, because Peavey had a few questions about the lay out and design of their Peavey Copies.
Earth Sound Research Started out as PLUSH amps, and then evolved into Earth Sound Research. .... And they did plenty of Research.

I don't think i've ever seen one of their amps that wasn't a Fender Bassman Or Peavey 130 series copy.