I'd almost be willing to bet, that it's an 8 volt bulb. Pretty much every other Marantz bulb is 8 volts.
As for amperage- what format is the bulb? Is it one of those fuse bulbs, a bayonet socket, or a "rice-grain" mini-bulb? Most of the fuse bulbs (the ones that look like a glass fuse) are 200 ma, most of the bayonet ones are 100-200ma, and the "rice-grain" mini-bulbs are usually 35 or 70 ma...
Regards,
Gordon.