The problem belong to the Eico preamp. My tech try to ground everywhere he should but never obtain results.
Power supply then!... (gosh!)

I hardly dont understand these ground problem on old appliances. With no electric ground (two prong plug) and no attach to the ground anywhere, how ground can be good? There is black wires attach to the body, yes, but is that sufficient?
How could I be sure ground is good?!

Thanks again