If I weren't so lazy I would dig out some service info, but off the top of my head, one set probably has 6 tubes and the upgrade model probably has 8 tubes. If so, the 8 tube model should have a "push-pull" audio amplifier section in it. The "push-pull" output features more power and lower distortion. If you are handy with a solder gun and can accommodate a 6 volt radio, the radio probably only needs its capacitors replaced and the set will work like new. Check your local public library to see whether they have Sam's Photofact files from the early 50's, of so, you have some pictures, a schematic, and a parts list. The Photofacts turn up on eBay from time to to time, too and can be had for for a few bucks. Sams has an index online to help you find the right one and will send you copies, but finding an original on eBay is cheaper.