I know that the 12U7 is the preamp section. I'm just wondering if it ends before or after R7 and R9.

And Phil, your design looks impressive! It's a bit much for what I'd like to do but looks like something fun in the future.

Hello! I'm looking for a low voltage tube based preamp. I've search around the internet and found a few schematics but some of them are schematics of both the preamp and power amp sections and in some cases, I'm unsure of where the preamp ends and the power amp begins. I'm also looking for a no frills design, so something clean (as clean as can be hand under low voltage) and no tone shaping. Also, I'm working with 15V from an old power supply that I salvaged and would like to use.

So far, this is what my search has shown me:
Sopht amps - http://www.sophtamps.ca/mambo/index.php?option=com_content&task=view&id=25&Itemid=37
Soul-o-tube - http://www.avwz35.dsl.pipex.com/soul-o-tube.gif
Tube Cricket - http://www.beavisaudio.com/Projects/TubeCricket/TubeCricket_Final_2008.gif

So far, the sopht amp seems to be the best option since it uses tubes that are actually meant to be run at low voltages but I'm unsure where the preamp ends and the power amp starts. Does anyone have any experience with any of these circuits? And how would I go about modifying them to be clean and have no tone shaping.

My final option is to just go completely SS and do the fetzer valve but I'd really like to go with tubes (partly for the aesthetic value and partly for the challenge of learning how to work with tubes). I appreciate all the help you can offer! Thanks everyone!

I've had to put my project on hold. Turns out I had a bunch of bad transistors.

Thanks for the debugging tips! Hopefully I can find the problem and fix it up. It's my first foray into DIY circuits.

Hello!

So I took a modified Fender Bassman 6G6-B schematic and borrowed some ideas from the Professor Tweed (using FETs and a low pass filter at the end) and came up with this schematic, which I want to ultimately use as a preamp for a DIY combo amp. I've kinda gotten stuck on it and can't seem to get it to work. I was able to biased the FETs to half the voltage (biased to about 7.5V from a 15V power supply). But when I try it out on my amp, I don't get any sound at all. Can anyone suggest why I'm not getting any sound? Will this hypothetically work at all right now?

Professor Tweed Schematic: http://www.runoffgroove.com/professor.html
Modified 6G6-B Schematic: http://web.archive.org/web/20020317060405/http://home.cfl.rr.com/dbhammond/baby_bassman.gif
My Schematic: http://www.freestompboxes.org/download/file.php?id=21284&mode=view

Here's the stripboard layout I came up with. I've built it but I don't get any sound out of it.
Stripboard Layout: http://oi49.tinypic.com/1zdlkl1.jpg