Look for a line fuse. Most larger units had them by the 60's. Should be located near where the line power comes into the chassis.
If it does have a fuse, and it has popped, keep in mind that fuses don't blow for no reason. Chances are the set has a bad filter cap in the power supply, or some similar fault that caused excessive current draw. Try amother fuse of the correct size; if it pops again in short order, plan to do some troubleshooting.
I think Astro-Sonic was a line made by Magnavox. Try a Google search with "Magnavox" and the model number of the set (paper label pasted on the back or inside). Radiomuseum.com may have some service info on this set.