Gary,
King came out with the Symphony model trumpet around 1949 and produced them through 1968 or so until they were bought out by UMI. The symphony Trumpets are all Dual Bore instruments with optional Sterling Sliver Bells and leadpipes. Harry James played on a customized version of this horn.
The Symphony model was a Super 20 model trumpet with a Dual Bore. It came with a brass bell and and sometimes the optional sterling silver leadpipe.
The Silver Sonic Symphony was a Dual Bore Super 20 with Sterling Silver leadpipe and silver bell.
They're all generally great playing horns with a very open blow and big sound.
There's a picture of my Silver Sonic Super 20 Symphony here:
http://www.trumpetmaster.com/vb/140/...tml#post310450 (VINTAGE HORN EYE CANDY)
Check out
H N White Company Makers of King Band Instruments 1893-1965 for more information.