Matsumin's Valve CasterMatsumin's Valve Caster is a tube boost and light overdrive operated from 9V DC. You could even use batteries, if you're rich.
The original schematic went missing and Beavis Audio resurrected it. The DIY Stompbox thread contains a lot of good information but can be a bit daunting (174 pages as this is written). Also look at Beavis own page about this circuit and variations of it.
LinksDIY Stompbox thread
Beavis Audio's Matsumin's Valve Caste page
PDF with everything Caster (Valve/Twin/Triple and Sub)
VariantsRenegadrians Twincaster - Two tubes, twice the fun.
Triple Valvecaster - Three tubes, thrice the fun?
About Sub CasterLooking at the Sub Caster in the PDF above, if you use a 6112 submini instead of the recomended 6111 you will want to change some resistors as FC noted
For a 6112 Subcaster: change R5 to 100k, change R6 to 100k.