Just an old hk tuner. Nothin' special; probably sounds decent when/if it's in good working order. Probably needs some attention at this late date "for best results".
You can probably find the manual at:
www.harmankardon.com
EDIT: yeppers, here it is:
http://manuals.harman.com/HK/Owner%2...ual/A200om.pdf
EDIT^2: looks like this tuner uses a half-wave selenium rectifier. That should really be replaced with a modern silicon diode (assuming it hasn't been already). This will require a little power-supply modification (extra dropping resistor) to allow for the more-efficient silicon rectifier.