1. It’s an excellent, very popular amp and great value for money but, out of the box, it doesn’t sound as good as it could because it’s made to a price and doesn’t always use the best quality components. By changing component quality and values the sound can be opened up and a wider range of tones can be achieved. Adding new components provides an even wider range of sounds.
2. It has a Master Volume and you can get breakup and distortion at low levels but it's not the creamy output tube sound with harmonics and sustain that you get when the amp is cranked up and 15 watts is just TOO LOUD for most people to be able to get the true valve distortion sound that they are looking for.
   In a medium size room, which is where most people have to practice, even a 1 watt valve amp can be so loud that you would have to shout really loud to be heard (about 100 decibels) - and around 1/10th of a watt is what is often referred to as “bedroom level” for late night noodling.

   By fitting Power-Scaling™ to your Blues Junior you can achieve any level and combination of pre-amp and output stage distortion down to less than 1/10th watt.
   ( see http://www.londonpower.com/pscaling.htm)

3. The Master Volume is very sensitive when you are trying to set it at lower levels which makes it tricky to set distorted tones at low levels.

4. The Reverb control is also very sensitive when you're trying to set low levels of reverb
5. The reverb in the early 'green board' models is wired differently than the later 'cream board' models - it's not proportional to the master volume setting.
6. The output tubes are nearly always biased too hot i.e. the output is set too high and
   there is no adjustment for the output valve 'bias'.  When you change output valves you MUST re-bias them if you want to:
   a) maintain the same tone or experiment with other tones
   b) extend the valve life
   The only way to do this on a Blues Junior is to have an amp tech change the bias circuit.  Even then you cannot adjust the bias on individual valves.
7. UK amps are often wired for the wrong supply voltage.
8. The Negative Feedback circuit has no adjustment (no presence control).
9. The Fender speaker sounds OK but it's a bit 'flabby' in the bottom end mainly due to issues with the amp.
10. Some newer amps have leaking Filter capacitors.

About our modifications

We can correct all of the issues highlighted above.

You will find a number of modifications for Blues Juniors on the internet.  The most respected site is that of Bill Machrone.  Our mods include some of Bill's published mods that are in the public domain.  We also fit Power Scaling with bias measurement points and adjustment for each output tube so that you can set the bias yourself.

I have chosen what I believe to be a successful combination of changes and additions which allow the amp to reach it’s full potential and provide a wide range of tones from clean to heavy distortion and all at volumes down to ‘bedroom level’.

*Please note that I am licensed to install Power Scaling™ and use genuine London Power components for the Power Scaling™ circuit.

Modification Options

We offer a range of mods to your own Blues Junior as well as ready modified amplifiers.

Please contact us to discuss the most suitable mods for your amp.

• Power Scaling™ 15 watts down to 0.1 watt of pure valve tone.
  (see the Power Scaling page and FAQ's).
  This also includes individual bias adjustment pots for each valve and bias measurement points so that you can adjust the bias yourself without encountering high voltages.
• Combined Power and Standby Switch.
• Audio taper Master Volume control.
• Audio taper reverb control.
• Green board reverb re-wired to cream board spec.
• Presence control.
• Tone stack mod to allow full reduction of mids (can be switchable with presence control).
• New top quality tone caps and other improved components.
• Shielding or replacement of the standard input jack.
• Bright mod to give a 'green board' amp more treble.  Not as bright as the 'cream board' but close.  Can be switchable with the presence control.
• Increased output tube filter cap for 'better' loud bass notes and less sag.
• Change to pre-amp voltages to improve clean headroom (best for 'green board' BJ's).
• Upgraded speaker to Celestion Greenback or Vintage 30.
• Upgraded valves to Sovtek or JJ's.