Hi;
Well i repaired radio's and tv's since 1965 until 1986. I'll try to remeber and tell what I know about this radio.
1st off write to zenith or email them. They have someone that can give better info, but I guess you didn't need me to tell you that.
I'd say you have a radio there about mid sixties, it has a string dial cord terrible to redo I've done many. Be careful not to break that!--They get loose and the dial calibration goes off-Best not to correct that, unless you've done dial cords before. You need diagram that will tell you how the dial cord needs to be redone.The frequency range is low VHF 30 to 50 and a high vhf range am and fm band. they used diode rectifier I believe 1/2 wave with a large filter capacitor. But it could and more then likely have full wave bridge rectifiers that I can't remember (Wheatstone bridge). The speakers are 8 ohm Pm ---cone brittle at that age, they had speaker coil problems where the speaker coil jammed and changing the impedence and blowing output transistors.
Excellant quality in those years and competed with german radio (GRundig) (Plaubunlk) came close but still I loved my german radio's Super sound.
The key point you have there is the frequency range, iT'S A TELL TALE OF THE RADIO--It wouldn't surprise me if it still played well
Excellant radio
if all else fails for information---google search the item
wilskro