Part of the later, export-only, Supreme series, the Model 500 is essentially a Model 600.
It is in fact the same amplifier, the same circuits, the same parts, the same everything with only less power output, less tape output level on both DIN and RCA terminals, and a 5dB recessed S/N ratio of the power amp section.
Dropped from the Model 600 is the front Phono 1 impedance 3-step switch which is put at the back on the Model 500 and reduced to 2-step ; what takes the place of that front switch is a Phono 2 0...-6dB gain knob.
Otherwise it is the same, therefore just as good, therefore just as excellent : Supreme !
As the Model 500 is a Model 600, please refer the latter's page for all the details and extensive TECH descriptions.
See the large two-page schematic of the Model 500 here.