I bought my YBA2 BassMate for the express purpose of making an 18 watt. I played it and decided to keep it stock. I bought a ElV6 from Coco instead.
One thing that kept me from doing the conversion was the 400+ volts on the power supply. That's way too much for an 18 watt. The next thing is the sand rectifier. No dropping any volts there.
Only three knobs on the chassis. It's a pretty cool design , really. The Volume is more like a "Master" with the "Vol" always on ten. The cabinet is a one fifteen (sealed). It makes for a clean sister to a dirtier 18 watt. Plus I can play bass thru it.
LeeMo
Check here:
http://www.informatik.uni-bremen.de/~da ... odels.html