1965 Magnavox Astro-Sonic model 2ST673

i just got this and the speakers on the left side barely put out any sound and when i turn the bass all the way up the woofer on the right side stops putting out sound. so my question is how do i figure out what the problem is. everything looks fine as far as i can tell. nothing looks fried and all the wires look fine. i don't know jack about electronics so i need help. i can replace the speakers but i don't want to do that if that's not the problem. and finally, if it is the speakers and i need to replace them, do i need to get the kind of speakers that are in there now or can i get modern speakers. thank you in advance for your help.

The speakers on those rarely go bad, so the simple thing to do is check the bias voltages of the outputs/drivers against the service info to see if their leaky/defective, and most likely do a recapping.