Re: Using the Tube Head with bass guitar
Most likely you won't have to change anything to get a satisfactory preamp. Something I always do with PAiA preamps is replace all of the signal capacitors with higher quality film caps or, in the case of high value electrolytics, Nichicon or similar audio grade electrolytic capacitors. You probably don't need to modify any of the values yet, I'd get the thing up and running with the stock values replaced first.
You may want to increase C12 and C22, this prevents any of the switching noise from the charge pump getting into your tube circuit. 47uF to 100uF is more preferable if you can fit the parts. Also, a mod I always do is to run the tubes off of filtered DC. Here is a link that shows you what to do (scroll to the bottom of the page): http://www.paia.com/ProdArticles/tmpmod.htm