In my project amp it sits right at the beginning. The guitar plugs straight into the cathode follower and the
circuit output drives the distortion stage. That's why I designed it to have gain. If you want it to have unity
gain, open-circuit R14, short R13, and change R1 to 33k. You also might want to try removing R10, it
doesn't serve any useful purpose. I put it in because I thought I needed a grid leak. 


regulated DC power for preamp tubes
I use Linear Technology's LT-1086-Ct, available from Digi-key. It
has variable output rated at 1.5 amp. Just fine for your preamp
tubes. They make a slew of em so you can get them with different
ratings and voltages out. Much better regulation than the LM-317
and 350 IMO.

A simple way to do this is to buy a 5 volt regulator
e.g. 7805, and connect 2 diodes in series between
the common leg and ground. This increases the
output voltage by 2 diode drops, et voila! 6.4
volts! If you're running your dual triodes with the
heaters in series, get a 7812 and add one diode for
12.7 volts.

The other way it's usually done is to get an
adjustable regulator, e.g. the LM317, and set it
using the right combo of resistors. You can get a
data sheet for the 317 on the Web:
http://www.national.com/ds/LM/LM117.pdf

One point to remember when selecting a suitable
3-terminal regulator IC: They have different
minimum voltage drops needed to maintain
regulation. The adjustable 317/350 types don't
require as high an unregulated DC voltage as the
78XX types for the same regulated DC output
voltage. If your raw DC supply is high enough, then
it doesn't matter, you can use either type. I've also
read that the 317 adjustables have lower noise than
the 78XX series. 

el84

By the way, I happen to like the way an EL84 sounds at about
325vdc to 350vdc and idling around 10watts.
28ma to 32ma is fine if the tubes have some way to limit the
screen current a bit.

10 watts at 300v would be:
10w/300v=33ma

Oh, and the voltage on the grid of a fixed bias amp is not the
same effect as the same voltage of bias used with cathode biasing.
The biasing resistor on the cathode can add some interesting tone
from negative feedback plus there will alway be slightly less
voltage on the plate when compared to the cathode if the cathode
is grounded rather then being held above ground by said bias
resistor.