This guy?
Never saw one of these before. One thing that might help... Heathkit would often "recycle" old electronics into new cases with little or no change to the guts. Perhaps a different Heathkit table radio would have the same circuit design?
How complicated could it be? :-)
EDIT: If you're desperate, Heathkit does still exist and does still provide support. They'd probably be happy to provide a copy of the original manual to you, but they will want $20 or so for it. You can send 'em an e-mail and ask.
www.heathkit.com