In 1960, Zenith produced a limited quantity of speaker boxes called the Converta (Royal 55C) to go with the Royal 50.  It’s purpose was to convert the shirt pocket sized radio into a table radio that produced a bigger sound through it’s 4″ speaker. 

It measures 6″ high, 7.5″ wide, and 3″ deep and weighs only 18 ounces.  It works well, producing a “bigger” sound, but with the radio installed, it becomes quite top-heavy and not very stable and with a fall or two, the thin legs would break, making it even less stable.  It’s cost was $39.95 - $44.95 (which did not include the radio) which made it quite an expensive option and thus not a hot seller.  They were made of brittle plastic and as a result, these are very difficult to find in good condition.

Check out these Royal 55C Converta radios.