Onkyo M-5550 is a japanese stereo power amplifier manufactured in 1989-1991. It is identical to M-502, produced on the different market. Higher model M-504 it’s also the same construction, only huge VU meters was added. Also the highest M-508 is a very similar construction. These all means that M-5550 (M 502) is a beast, is the cheapest and sounds practically the same like his older brothers.
This amplifier needs (if it is in original state) some minor repairs. After 30 years several capacitors need to be replaced, especially these 330uF which are very close to resistors and work at the high temperature. In mine these capacitors had a half of their nominal capacitance and huge Vloss.The BIAS should be corrected too.
After small service Onkyo plays and sound beutifully – very good choice for a price.