Read this WikiPedia Entry, come back, and we’ll talk.
For many, the Dumble amplifier is the holy grail of electric guitar tone. Its caché is helped by the rarity of the actual amplifiers and the famous (and talented) guitarists that favour the amp.
Mr. Dumble is apparently very secretive about his amplifier circuitry and most amps have the preamp components covered in a tinted silicone rubber. Consequently, there are very few fully documented Dumbles in web-land. One exception is serial number 124 which was extensively photographed and discussed by “Ayan” on the AmpGarage Forum. The photos are still available through links on the forum, but they are perhaps more easily accessed on Rob Livesey’s Page.
Number 124 was a non-HRM model and departed from ‘traditional’ component values noted in other Dumble’s of the time… but it has recently had some traction with forum members in their builds.
Brian did a full schematic of #124 recently which is posted in this thread on AmpGarage. But, for your viewing pleasure… attached is the PDF! Dumble #124 Schematic (PDF) This is one example of a D-Style Amplifier.
If you want to learn a lot more about Dumble Amps, including lots more schematics, layouts, BOM, discussion, sound clips, etc. The one and only place to go on the internet is the AmpGarage Forum.