Here is a simple Tube Overdrive/Boost pedal that can be built in a weekend if you have enough materials laying around (or if you spent some time & money and sourced the materials commercially).
It is based on Matsumin's ValveCaster, which has plans and a discussion thread a mile long on DIYStompboxes.com. Unlike Tube Amplifiers, this is a simple 9-12 Volt circuit, and can be built for under $50 (not including tube). It sounds incredible between a guitar and both tube or solid-state amplifier. It is versatile enough design that you can incorporate other effects into the same pedal, or go beyond for more stages. Take a listen to one of these builds, courtesy Dovinia:
(I would post a video of my own, but I am still a n00b at playing the guitar. I have had more fun building this stuff, and watching the reactions of regular players who get a feel of the tone of this thing with their own playing.)
Here are a couple of more links with others builds of the same design:
Some sweet licks and tone on a one single tube
Not enough? Go for two stages of gain!
Or even more...here are 3 chained together
With enough love and care in the manufacturing process, you could have a world-class tube overdrive pedal that is completely unique in design, and sounds just as good as one of the expensive boutique tube-overdrive pedals out there. Here is what I created and painted in my garage last winter which I hope to post videos of soon:
The name just stuck...It's a 12AU7 tube pedal running with a starved plate (cold) at 9-12 volts, while the 12AU7's specifications are designed to operate at over 200 volts in an amp.