Help me on a small tube effect

[bluefoxicy]

Hi, I'm having a little trouble understanding this circuit. Part of this is non-experience with a 12AU7, part is I have no real theory and so every time I take a few months break I don't have a f@*king clue about any electronics anymore.

Beavis Audio Research

There's no full explanation of this circuit. Anywhere.

I get the LM317 thing (that was a mod I was gonna do, then i scrolled down and -- oh nice!), but the tubes I don't get.

What's getting me here is the 12AU7 running (first off on 9V and not 18V or dual 18V or 330V) with a 50k cathode bias resister on stage 1, and no bias on stage 2. My interpretation of this is "stage 1 clips under, and stage 2 clips under more since the signal is inverted!" i.e. this should be very lopsided; consider the circuit I'm used to for 12AX7 preamp involves anywhere from 680 and 820 ohms to 2.2k and 2.2k for stages 1 and 2, plus a bypass capacitor of around 1uF to 22uF.

Maybe I'm just comparing it to a guitar amp too much, and expecting that the optimal sound would come from (besides giving a decent voltage) biasing the tubes properly and putting the "gain" pot as a 500K or 1M voltage divider between (top diagram) C2, V1B[7] (center pin), and R4.

Perhaps for this application, the proper place to place the gain control is on V1A[2] and static set the voltage divide such that slightly less than 5% of the signal passes to V1B[7]. In this case, since 12AU7 has 20x gain, when you barely START to clip, passing 5% of the signal would push the second 12AU7 gain stage to barely start to clip too; pushing, say, 4.75% would let you get a little first-stage distortion before making second stage distortion, while passing 4% would mean you'd have to go for a gain of 25 (clipping at 20) to start distorting the second stage. 1M to ground, 40k to grid?

Anyway anyone care to comment and explain the likely theory behind this circuit, particularly the placement of Gain and the wisdom of R2 and R3, as well as the lack of a cathode resistor on V1B?