My experience is the value of most of these old systems is usually intrinsic. The value is knowing that your grandfather owned and enjoyed it. It is retro and a cool conversation piece. Those are the things that make them valuable.If you must put a dollar figure on it, console stereos like yours are usually worth $50 - $500.
There are some collectables that are worth more, and you can find info on them with a little bit of searching. Old Macintosh hifi equipment, Western Electric, Altec Lansing and RCA theater systems are sometimes sought after, depending on model. There are others; Those were just some examples.