Cool!!! Any soundclips? I have only one tube, and don't know what to built with it, so I ask for soundclips to know how it sounds.
No clips yet, but it sounds pretty nice. On the overdrive side it is a bit raspy, but I think that could be tamed with some filtering caps.
Anymore pics of the whole circut?
Will try and box it up tonight for pix!
but 12au7....can this be a 12ax7 in this case?
If I remember correctly, the relative gain of the 12A*7 tubes goes something like this:
12AU7 20
12AV7 40
12AY7 50
12AT7 60
12AX7 100
I built it wih the 12AU7/12U7 as specified on the schematic. I tried a 12AT7 and it was too much gain and sounded really bad. I also tried a couple of 12AX7s and it sounded even worse--pretty much unusable. I'm not really very knowledgeable about biasing tubes, but I suspect using an AT7 or AX7 will require resistor value changes.
After a little more research, it seems that au and ax are correct pin for pin, and the ax has about 7x more gain than au. However, i dont know if it is possible to run the ax in this circuit due to 9vdc?
From the little I know, you'll probably want to go up to 12vDC to use the AX7. Here's a diagram for using a 12AX7 as a clipper pair based on info from another thread here:

So 12 volt to heater 4 and heater 5 to ground might work.
He moved his site recently to a new address http://www.matsumin.net/
Thanks very much for the link! I'll update my schemo tonight to add the new URL.
Nice work dano! I was wondering, what needs to be changed say I want to run this at high voltage?
I think this design made the usual compromises to run at low voltage. If you are going to create a tube boost/overdrive and are using high voltage, that are lots of better designs out there.
Thanks to Matsumin for this fun circuit.