Blues Jr. Mod!

 The Fender Blues Jr. is a classic little tube amp. It's got 15W of power, a 12" speaker, two el84 power tubes, three 12ax7 preamp tubes, a spring reverb tank and one channel with boost/Fat mode. The volume, master and fat controls allow you to dial in some OD tones at low volume levels as well as keeping the amp clean at higher volume settings. The 3 band EQ is also pretty useful.
 The Blues Jr. is all about clean tones though. There are some semi-distorted sounds available but don't expect lots of gain and lead. There are many mods one could do to this little amp but we decided to stick with the basic Billm mod kit for this one. The basic kit does require some soldering skills and a bit of experience on valve projects. It's definitely not designed for beginners.
http://billmaudio.com/wp/
 The basic steps to complete the modification is to remove a few "stock" components: tonestack and power capacitors, on/stand-by switch etc. Then, you can replace them with the ones supplied by Billm. The new capacitors can really make a difference as the clean tones get much more refined and the OD/boost tones become more responsive and sweet. The amp can now deal with od/dist/boost pedals a lot easier.
 One thing you have to avoid while modifying the amp is overheating the pcb, the traces or the new components. A simple low wattage soldering iron is just right for this type of work as the circuit board is really sensitive and the metal pcb component pads could fall off should you apply too much heat on them. Make sure to check every solder joint or pad for continuity using a digital multimeter (DMM) with a buzzer/Ohm-meter.
  There are many other mods one could do to this amp and some may apply to other 15W amps as well. So, do your homework and maybe you could squeeze better tones from your guitar amp. Just don't forget that there are HIGH VOLTAGES inside any valve guitar amp and most high power solid state amps even when they're turned off...

Here are a few pictures of the Blues Jr Billm mod:

Cheers,
Thanos