One of the easiest mods you can do your Blues Junior is to convert the tone stack from standard operation to Twin-style operation. Here’s the deal: The Twin is renowned for its bell-like clean tone. Part of that is having enormous power and headroom on tap, but the way the tone stack is wired contributes to the bright, Twin clarity. In the Twin, you can turn the bass, middle, and treble to 1, and get no sound out of the amp–all frequencies are cut off.
The Blackface tone stack, by comparison, started out with just treble and bass–and a fixed mids resistor. No matter how much you reduced the bass and treble, some mid-frequencies are always present. The Hot Rod series of amps, of which the Blues Junior is a member, added a mids control, but in a nod to earlier Blackface amps such as the Deluxe Reverb and Princeton Reverb, turning the mids control to 1 still left a basic amount of mids in the mix.
The surprising thing is how bassy the leftover mids are and how much they can muddy up your tone. Fortunately, it’s incredibly easy to modify the Blues Junior tone stack to work like the Twin’s. The reward is greater tonal flexibility and cleaner, brighter cleans and more interesting distortion tones. Of course, this works best with the tone stack mod, replacing the wimpy values in the Blues Junior stack with premium capacitors that give more solid bass–and mids.
This mod gives you all of your stock Blues Junior mids tones from about 4 and up on the control and fewer mids, down to none, from 4 and down to 1. It opens up the possibility of an ultra-scooped tone, with just treble and bass, as well as bass-only overdrive, which can be very effective by eliminating middle and high harmonics.
Don’t get me wrong–the Twin is still the King of Clean and no 15 watt amp can pretend to be something it’s not. But this mod is dead easy and opens up some very nice tone possibilities. It’s a popular mod on the Blues Deluxe, Hot Rod Deluxe and Deville, for the same reason. So try it!
All you have to do is connect the left and middle (looking from the back) terminals of the mids control together. This allows the mids control to fully ground out the middle frequencies. You can bend a short piece of wire and stick it into the eyelets in the back of the control. You don’t even need insulation. A piece of bare wire will do fine.
You must, however, make sure that the jumper wire is not longer than the eyelets’ depth, otherwise it could short against the metal portion of the control, which would remove all of the mids. You must also take care not to overheat the control. Use a deft touch with the iron–just enough to melt the solder and fuse to both the wire and the eyelet.
This mod is shown on a cream board, but it works equally well with the green board Blues Junior.
Just to restate one of the points above, the TwinStack will give you a noticeable improvement on any Blues Junior, but the tone stack mod brings out the best by providing more available bass and mids. With more mids on tap from the tone stack, you have more available when the control is wide open, down to zero when the control is at 1. So you improve on the stock tones at both ends.
When we do this mod in the shop, we bridge the center and left mids pot terminals on the back of the board. If you’re going to be pulling the board to install other mods, plan on doing it from the back; it’s faster and easier.
Here’s how: First, start with a short scrap of wire that bridges the two left pins of the mids pot. A thicker clipping from the tone caps or power supply stiffening caps is perfect.
Next, apply heat from your soldering iron to the middle of the wire. Add a little bit of solder if necessary to help the melt.