[quote author="bradb"]I've been searching here for details but can't find anything, there must be some information on the REDDI?
No?[/quote]
The tube direct box?
It's still commercially available. Musician's Friend has it: http://www.musiciansfriend.com/product/ADesigns-REDDI-Tube-Direct-Box?sku=189904
Well it only uses one dual triode valve, so its probably input amp, output control, transformer line amp.
It could be either a cap coupled or direct coupled to the output transformer.
Its says its based on the sound of an Ampeg B15, not that its based on the B15 circuit.
Sorr