Google is your friend. Please, Vinhoff, post something with a source, rather than something you heard.
From the Unofficial Earth Sound Research site:
The following is an E-mail I received from Andy Fuchs
He said I could post it here so .....
"I worked for them for about a year. They were an interesting company.
There's a website at www.plushamps.com or is it www.plush-amps.com (I
forget which), which covers their sister company. I believe that Plush
became Earth after they moved to California and I think Earth bought the
remains of what was left in the NYC factories. I worked for one of a
number of subcontractors who actually built the Earth gear for them.
They never actually had their own factory (that I'm aware of) , but
rather ended up making their stuff at various subcontractors. They used
a few around the NY/Long Island area, and mostly copied Fenders (for the
Plush and later Earth stuff that looked like it), or Peaveys. We
actually used Peavey schematics in the shop for service ! The biggest
problem was, they copied Peavey, but used inferior output transistors.
Sad part was, that everything else was equal (or in some cases better)
than the Peavey counterparts, but the outputs failing hurt them as many
amps came back for service or repairs. They used a high-grade military
subcontractor (Qualtrol Electronics in Deer Park), who built vending
machines, and military aircraft electronics. The metalwork and circuit
boards were copied from Peavey, and duplicated very accurately. Peavey
was planning to sue them (they actually flew one of our technicians to
Mississippi to interview him about the whole process), but the end
result was Peavey's attorneys advised him to change the models to new
designs, as it would be cheaper than suing Earth.