Here's the layout for a tube overdrive pedal. It works great I tell you that much, and you can make one for 35 bucks or so. This is based on a schematic I found, I tried to make the layout as straightforward as possible, also inspired by a similar layout I found. It may sound difficult because it's a tube project, but if you can solder a LP harness you can do this. There's absolutely no difficulty. You can mount the tube anywhere, it's a regular 9 pin socket. Because of this, you can also replace the tube or experiment with different brands to get a better tone. I used this with my Marshall and it kicks ass, I mean it, and I'm using a crappy generic tube I found on sale for 4 bucks. It also works with a 9V battery or a power supply, can't get any more convenient than that. Currently thinking about a dual 12AU7 version for even more options. Enjoy.