Ever wonder what the model number of your Zenith really means?  Near as I have been able to figure out from original factory service manuals, there was a coding system they used.  Say your radio is a R500YH model.  Here is how it works. 

R = Zenith Royal line, 500 = Radio’s family #, Y = Color, H = Radio’s model

Here are the color codes Zenith used with their transistors:

B=blue, C=Charcoal and brown, F=turquoise and two tone green, G = grey, J=two tone brown, L=tan and beige, P=yellow, R=maroon, V=red and coral, W=white, and Y=black. 

Thus, the example used above of a R500YH would be a black Royal 500H. 

These model number codes were printed on the stock boxes for identification

They were also put on a sticker on the outside of the radio on the bottom 

 

With some models, they put the sticker inside on the back half. 

 

This sticker also has the serial # of that particular radio.  I feel it is a plus to have a radio that still has this sticker in readable condition.

Hope this helps you.  So now go look for those stickers!   

Check out these Zenith Royal Color Codes radios.

sticker on box
sticker on outside
sticker inside