Quadraflex was a house brand of "Pacific Stereo" I believe.
I do not know whom made the equipment. I personally would look something along the lines of a 70's SS receiver. I really like the Kenwood KR series of receivers. Pioneers were also very nice. Your old Quadralex might need to have the tubes replaced. The sound of the newer Yamaha receivers might not be to your liking because they will not sound anything what you've been listening to for so long.
I do not know whom made the equipment. I personally would look something along the lines of a 70's SS receiver. I really like the Kenwood KR series of receivers. Pioneers were also very nice. Your old Quadralex might need to have the tubes replaced. The sound of the newer Yamaha receivers might not be to your liking because they will not sound anything what you've been listening to for so long.