On this page are several postcards which show radios, or related subjects.  The first card was mailed in Amsterdam in 1931.  This is interesting because the radio shown is a crystal set of a design that was very much obsolete by that date. 
This card was printed in the Netherlands and was postmarked in 1926.  The radio is a three tube model, with the tubes exposed on top, as was typical in European designs of the 1920's.
Above is a Valentine card from the mid 1920's.  The heart is edged with glued-on glitter which doesn't show up well in this scan.
This card is an obvious takeoff on the Victor dog, Nipper, but the phonograph has been replaced by a flask of whiskey and a funnel.
This card is from 1947 and shows a television production scene from WRGB, Schenectady, NY.
This early radio-related postcard was mailed in 1910, and promised to reveal a secret "wireless message" once the recipient rubbed a pencil across its surface.  The message was printed using a type of ink that would absorb and hold the pencil lead.  It was less reflective than the surface of the paper, so when held properly, the message can be read without damaging the card.  Like the kid in "A Christmas Story", I was also disappointed to find that this was nothing but a "crummy commercial".  In this case, it was an advertisement for a bank in Scranton, Pennsylvania.