This is the circuit. The first stage is very similar to matsumin's circuit except that I switched the 220k and 100k plate resistors around. The second stage has a high value resistor on the first plate to increase the gain of the triode. The 100k resistor on the other plate amplifies the volume again so that it isn't extremely quiet. The gain of a triode is directly related to the value of the plate resistor (among a bunch of other factors) because a larger resistor limits the current. Limited current increases the voltage drop when the tube when the tube is conducting, this increases the gain. I put 330k-680k on the schematic because anything in that range gives really good gain. You could of course go higher than 680k but I choose not to because it was too much distortion for my liking.



There are three pots shown, the volume pot on the right which says 10k-50k audio. It should be an audio pot for the best volume control. I used a 10k pot but you can really use any The other two pots are gain pots. They control how much gain each stage of the circuit has. I only included the gain pot on the first stage, but I would put the second one in if I could make a second pedal. I used a 10k pot for the gain control but it doesn't provide noticeable difference from high to low. A 50k pot would work much better.



I found that the values of the capacitors doesn't have too much of an effect on the circuit, neither does the values of the grid resistors. You have some freedom for values there without much worry of something not working.



If you would like to add a tone pot, put a 10nf capacitor and a 50k--100k pot in from the output of the second bypass switch to ground. The capacitor should be after the 1uf capacitor but before the volume control.