Where can you find component drawings/specs for 60s - 80s audio equipment?

I have a fried pot from Alps (981n-250k bx2). I could replace it
if I could find a spec. (Snooped around Alps site but nothing.
Send a request for info... lets hope)

Thanks

I'd get an old service manual but that's worth 20 of these parts.
akai aa-r20 receiver