The overall design influence of the Sony TR-6 can be seen on this and other horizontal sets of the same era. Indeed, the easel stand that allows the user to lean the radio back several degrees is remarkably similar to that of the TR-6. Granted, Hitachi did refine an existing concept, making the stand a little beefier while also adding supports on the bottom of the radio to help ensure stability when standing straight up.

In another move that seems to follow revisions at Sony, Hitachi dropped the easel stand from the back of the TH-668, the successor to the TH-669, in the same manner as the TR-66 replaced the TR-6.