If you find these, you can be relatively certain that the radio was produced during the period of 1955-1963. However, that isn't the only clue, and cannot be relied on exclusively. Electronics changed considerably over the period of radio manufacture. Transistors, specifically, look different in older radios, often being of oval shape, or having steel cases which resemble top hats. Radios which contain black plastic encapsulated transistors are from later, after the mid-1960s.
Cabinets offer a wealth of information, too.
Finally, also check to see where the radio was made. If it was made in Japan, the U.S., or Europe, chances are it is an earlier model. Back to top 7. A popular question, and a difficult one to answer, as the market for transistor radios is extremely volatile. I recommend some of the guides on my Recommended Reading page for general valuations.