Orange TT bias??

[Guitar-Sam]

K for going on 4 years I've had an Orange Tiny Terror.Nice little amp,for getting decent tones at stage volume.IMO sounds like a Vox with JCM 800 gain. It has two 12ax7s and two el84s the volume is placed after the PI tube.
Anyway it has a 7W/15W selector on it which I'm pretty certain selects between two taps on the power tranny. I know the sticker on the power trans shows,one leg puts out 250V and the other puts out 185V. I read once on a forum that to get a happy medium one setting makes the bias a little cold the other a little hot.
What I notice is 15W is a little harsh and stiff feeling and 7W is a little too mushy and muffled.
What would I have to do to get it sounding and feeling right on 15W and how would I go about doing that?? Like what components would need swapping and how would I determine the values(expierament??)?
My amp modding skills are fairly limited as I've only gotten as far as the pre-amp of a Valve Jr once.I can read and(mostly) understand a schematic.
Here is a copy of the schematic:
http://thmq.mysteria.cz/diystompboxes.com/OTT/TT15.jpg" onclick="window.open(this.href);return false;

[Guitar-Sam]

I ended up finding what I was looking for. I need to reread it but I guess I just need to swap out the 180k cathode resistors for 100K or vise verse(like I said gotta re-read it) Now to get off my @ss and do it.