Determine the tube number and purchase a replacement vacuum tube. The number is printed on the tube’s glass body. The effects pedal owner’s manual will also give recommendations for replacement tubes. Do not touch the replacement tube until you’re ready to put it in.
Turn the pedal off and disconnect it from the AC outlet. If it’s been on for a while, allow 20 to 30 minutes for the tube to cool.
Read the pedal owner’s manual for the recommended instructions to remove the tube. The pedal may have a simple access door to let you replace the tube, or you may have to take the pedal’s case apart. An access door will open by loosening one or more screws. If you have to disassemble the pedal, use the screwdrivers and pliers to carefully remove the knobs, nuts and other hardware. Set the pieces aside where they won’t roll away or scatter. Unscrew and open the pedal chassis.
Remove the tube sheath if it has one. This is a metal tube that shields the glass vacuum tube. It may twist off or you may need to unscrew it with a screwdriver.
Remove the vacuum tube by gently wiggling it back and forth while pulling straight out with moderate force. Do not twist the tube.
Put on the plastic gloves. They will prevent oils from your fingers getting on the glass and causing the tube to heat unevenly. Open the box for the new tube and grasp the tube. Align the pins with the tube socket and press it in gently until it’s completely seated.
Replace the tube sheath, if necessary, by slipping it over the new tube and twisting it into its base or by tightening its screw.
Close the access cover and tighten the screw or reassemble the pedal chassis.