Fender Blues Junior III mods


Fender Blues Junior

Fender Blues Junior

Like many guitarists, I am the proud owner of a Fender Blues Junior amplifier. Picked it up for a song when a major Australian music retailer went bust a while ago. It’s a nice little amp but many people on the interwebs complain that, stock, it sounds “boxy” and lacks bottom end. This is mainly a symptom of cramming a 12 inch speaker into such a small cabinet. Fortunately there are plenty of ways of improving the sound.

Now let there be no mistake. Most of the simple modifications I performed were suggested by a gentleman named Bill M. who runs the definitive website for Blues Junior mods. Check it out if you want the full story. He sells kits and offers support. I’m simply documenting the inexpensive mods I made mainly so I don’t forget. It goes without saying, don’t attempt any of these unless you know what you’re doing. And if you know what you’re doing, make sure the components are rated for the correct voltage.

My mods were performed against the Blues Junior III schematic.

Tone Stack

Increase bass response by replacing C6 with 0.1uF and C7 with 0.015uF.

Coupling Capacitors

Increase bass response by replacing C2 with 0.01uF and C8 with 0.02uF.

Power Supply Filtering Capacitor

Reduce lag by increasing C25 to 100uF. In my case Jaycar didn’t have one in stock so I added another 47uF in parallel.

Cooler Bias

Change R52 to 27k.

And there you have it. I haven’t gone as far as replacing the stock “Lightning Bolt” speaker yet, but I’m very interested in trying an Eminence Cannabis Rex…

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