Dumbles started out as Fenders but changed radically. The power supply is very beefy with solid state rectifier and lots of filtering and the tonestack is very unique. The design also uses "cascaded stages" to produce preamp distortion. Not completely unique, but not exactly the same as other designs.
Quite a few designs were lifted right from tube reference manuals. I believe some Fender designs were. And Marshall started out copying Fender. It could be that the granddaddy of all tube amps is Western Electric
The other interesting part of this is that every Dumble was different and tuned for the owner and what they wanted. All the Dumble cloners or Dumble inspired builders probably have a different Dumble in mind when they try to reproduce or build off that tone. So, the ear of the builder is pretty important.