I've just switched off the C30 after testing the mods I did and... wow! it does work! 
Now it got a REALLY good sound on the clean channel, very Fendery.
It has a Twin-like frequency response, with slightly scooped mid, sparkly at the right point with a lot of "dong" on the bass side.
Ok, it's not a Vibrolux, but for the money and the work I did it has more or less the type of sound I was lookin for.

Here are the things I did:

* took out C10 and R10 
* changed R6 with jumper
* changed C8 with a 33K resistor and R10 with a 1M Resistor
* changed R1 with a 100K resistor
* changed the slope resistor R19 with a 100K R
* changed C18 with a 100nF 
* changed C19 with a polystirol cap, same value
* put a 330K R across the 1M bass pot
* put a 15K R acorss the 20K Mid pot 
* changed C11 with a 1nF cap
* changed R12 with a 1.8M resistor
* changed R7 with 470K
* lit up a cig after the work

the boost now pumps the mids a little and it's, at least, usable.
I made a mistake, I've done all the things together, so I don't know exactly, for example, how R7 changes the tone.
But I'm really happy with it so, as soon as possible, I'll record something and I'll put it on my site, to let you hear the amp.
I'd like to thank you all for the help, especially Steve and Chris.
bye everybody,

Marcello



From: Marcello   (dt9rNOSPAMPLIZ@hotmail.com)
Date: 7/22/2002 5:39 PM
Subject: even more on Peavy C30 Mod :-)


Hi,
 
I've passed my weekend (well, not entirely...) opening, soldering, closing,
hearing, reopening, desoldering, soldering, closing... and so on, the c30 (much of
the time assembling and disassembling the chassis, as you probably could
imagine).
That's what came out...
- switched to 5751 for the first and the third tub, to a 12ax7wa for the second.
Very good!
- the 100K plate resitor in every stage seems to work really well, opening the
dynamic
- a 22M R21 (in place of the original 2M2) has a subtle effect on the dynamic
too
- switching to 100 nF 400V poly cap C6 increases the bass articulation a bit
- raising R18 has a negative effect, the sound is not as good as it was with the
original 1K5 resistor
- lowering C52 has a HORRID effect on the OD channel, that becomes a buzz
saw gizmo, plus the Normal channel resonates a bit too much, I still wondering
why. In the meantime a put a 1nF cap there (I don't know where the hell a put
the 1n5 cap and I haven'got any other) but I have to lower the treble to '3' to get
a full sound.
- I'm still not sure about the feedback loop (in or out), now, however, i put it
back stock
- switching to a 47n C19 and paralleling VR6 with a 10K (and not a 15K) let
the tone controls work a little better; with the mid full clockwise the configuration
is equal of a fender ab763 normal channel tone stack.
 
Ok, I decided next time (don't know when) I'll try the Tweed Mod... at least
when I'll find someone who sell that mini pots, since I can't find chicken knobs
that suit larger pot heads (I could drill larger holes but... I don't' know)
One thing for sure, I'll raise up the voltage of the pre, because the lower gain of
the tube opened the sound a lot and a higher plate voltage could increase the
tone further more.
 
with regards,
Marcello