All started with National...same company that invented the resonator guitar about 1929.
By the 50's, National had gone through differant owners and ended up evolving into Valco.
Valco made Supro products and also products for Sears (Silvertone) and Montgomery Wards (Airline).
I have a National Style O Resonator from about 1930 in my collection. And also a few wonderful Lap Steels that all have differant body shapes but use the exact same pickup assembly and have Supro, Silvertone or Airline on the headstock. Ry Cooder uses the pickup assembly off of these guitars as the bridge pickup in his favorite Strat!
If a guy is looking for a killer and inexpensive vintage Lap Steel get a Supro, Silvertone or Airline. Just make sure you're getting the right pickup.
The Silvertone Twin Twelve is a cool amp. I've owned three of them. Stock speakers are usually quality Jensen 50's C12Q speakers...same speaker that came in my '58 Fender Deluxe amp.
The Twin Twelves have a great swampy kind of tone...killer for rootsy music. Swampy is how I describe it. Probably the worst reverb I've ever heard....the springs are in a little box about 10" long. Sounds awful...but the vibrato is really cool!
My brother Bruce goes through those Silvertones and redesigns them for a much ballsier and better tone. I love mine and my buddy AJ gigs with his!
They are all point to point wiring: NO CIRCUIT BOARD!
Anyways, Valco and Danolectro both made high quality products in the 50's for musicians on a budget. Good stuff...though not the same quality as Fender or Gibson of course.