How to Upgrade the Amplifier Tubes on a Fender Blues Junior


The Fender Blues Junior is a 15 watt tube amp. According to Fender, it is the world's best-selling tube amp. There are various limited edition versions of the Fender Blues Junior that are distinguished mainly by cosmetic features such as the color or grille design. The Fender Blues Junior has a distinctive, "punchy" tone. To customize the tone or replace worn tubes it's essential to know how to upgrade the amplifier tubes on a Fender Blues Junior.

Things You'll Need

  • Screw driver
  • Latex gloves
  • Replacement tubes
  • Purchase your tube upgrades. The Fender Blues Junior comes with 3-by-12AX7 pre-amp tubes and 2-by-EL84 power tubes. If you bought amp used, the previous owner may swapped these out. The choice of upgrades is a matter of personal taste. If you want to alter the tone, consider a specialist tube manufacturer like Groove Tubes. Check the specifications of the existing tubes and replace like for like in terms of power. If you don't want to alter the tone and only need to replace worn tubes then get the same make and model as before.

  • Turn off the amp and let it cool down. Simply moving an amplifier when the tubes are hot can cause them to shatter so never attempt to remove tubes until at least half an hour has passed since you've turned off the power. Remove the plug from the outlet.

  • Remove the back panel to access the tubes. Unscrew the screws that fix the back panel to the cabinet. Place the screws on a flat surface so they don't roll away. It's easier to screw them back in to their original hole so place them in order. Once the back panel is off you will see the tubes.

  • Remove the existing tubes. The Fender Blues Junior is typical of many tube amps when it comes to tube housing and attachments. If you are replacing a burned out tube, look for the tube with the discolored filament. Lift the tube upwards only, don't twist it. The tube will simply pop out from the socket. Discard the old tubes in a safe manner as you would other glass items.

  • Insert the new tubes. Put on a pair of latex gloves. This prevents skin oil from getting on the surface of the tube. If skin oil gets on the glass it creates a hot spot which draws heat from the filament and causes the glass to shatter.

  • Test the amplifier. Turn the volume down low and power up the amp. Strum a few chords to make sure the amp is working. If there is no power or minimal volume, power down and make sure all the tubes are fitted correctly.

Tips & Warnings

  • Buy your tubes in bulk so that you always have spares of the same spec.
  • Consult the user manual if you plan to bias the tubes.
  • This amplifier carries a fatal amount of electric current, consult a professional if you are unsure about anything.

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  • Photo Credit vacuum tubes on white background image by Dmitry Rukhlenko from
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