Fender Blues Jr. Bias Kit

Fender Blues Junior amps have one major design flaw. They use a non adjustable grid bias in the power stage, and it’s set far too high. We’ve seen as high as 130% idle bias on units straight out of the factory. The valve PCB gets cooked overtime and the EL84s life greatly shortens. This kit ensures maximum output valve life and ensures that the main PCB doesn’t get carbonised.

This is an easy to fit kit which adds fully adjustable bias to your Fender Blues Jr.

This Blues Junior Bias mod kit is designed so that in the unlikely event of the pot wiper going open circuit, the power valve grids swing negative, saving the valves. Much of the advice on the internet about doing this mod misses this critical point. Other mods tend to leave the grid floating up towards GND in the event of pot oxidation, which will destroy the power valves.

We have partnered with Keld Ampworks for this mod.

If you’re buying this kit, your amp probably needs fresh EL84s since the current ones are likely worn, especially if they’ve been under-biased.

We offer the kit with JJ and Sovtek options, including a kit with the bombproof Sovtek EL84Ms.

Click here to see our Fender Blues Jr. valve kit options with medium and full gain valves.

Check out this YouTube Video to see how to fit this board. Super simple. Click here to download the installation instructions and see how it is done.

Fitting just consists of snipping out two resistors and a bit of glue to hold the little board down.

NOTE: Valve amps retain lethal voltages even when powered down and unplugged. DO NOT attempt this yourself unless you’re experienced working with high voltage electronics. If not, take it to a qualified technician. Stay safe.