How to Fix or Replace Your Preamp Tubes and Power Tubes

Tube/valve amplifiers produce a precise and dynamic sound that many musicians find desirable. The problem arises when the tubes age or occasionally blow/break. Whether your preamp tubes are producing inferior tone, or your power (output) tubes lead to power failure, these instructions will clearly outline how to diagnose the problem and fix it. The model used for these instructions is a Valve King VK100. This is a basic guitar amp head that resembles other models such as the Peavey 5150, 6505, and other tube heads.


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    Identify the problem. Are your power tubes the problem? If you answer yes to any of the questions below, your power tubes may need replacing. These tubes are the larger unguarded tubes located in the middle of your amp.
    • Is there a crackling sound or volume fluctuation when the amp is in use?
    • Does the amp fail to turn on when the power cable is connected to a working outlet?
    • Are the tubes glowing unevenly?
    • Are burn marks or cracks on one or more of the power tubes?
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    See if your preamp tubes are the problem. If you answer yes to any of the questions above, your preamp tubes may be the problem. These tubes are smaller and located at the sides and front of the amp and they have a small aluminum casing surrounding them.
    • Are the power tubes in seemingly working condition yet your tone or volume seems bland or quiet?
    • Does a crackling or screeching sound change when you adjust the volume knob?
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    Purchase your tubes. Look at the instruction manual for information on compatible tubes for your amp. These tubes are best to buy in pairs with matched ratings.
    • Discuss your tube options with technicians or salespeople before making a purchase in store.
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    Turn off the amplifier and unplug it from the outlet. Wait about 15 minutes before maintenance. The tubes must be cool and uncharged for safety purposes.
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    Unscrew the protective cage on the back. The screws will be located on the side of the head, or on the back of the cage itself.
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    Handle all tubes with caution. Use gloves or a cloth to handle new tubes. There is some debate going on about the influence of oils in human skin on a tube. In addition, there is no harm in wearing gloves to change tubes so it may be a good exercise in caution.
    • Do not place tubes near any ledges. The round tube has the tendency to roll around so use a cloth to place under them.
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    Remove the affected power tube (if necessary). Firmly grasp the tube with one hand and press down on the clamp to provide room for the tube to move.
    • Gently rock the tube back and forth while lightly pulling upwards.
    • Note the positions of the pins on the bottom of the tube. There is a plastic nub in the middle of the bottom of the tube that fits into a guide in the socket.
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    Compare the pins on the power tube with the corresponding socket and line up the nub with the guide inside of the socket.
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    Place the power tube into the socket and gently rock it back and forth with minimal pressure on the tube.
    • Press on the clamps if needed to ease the tube in.
    • When the pins are no longer visible the tube is in place.
    • If you plan on replacing the preamp tubes as well, leave out any power tube replacements that may crowd the area you are working in.
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    Remove the affected preamp tube (if necessary).
    • Remove the screws on the metal covering that encases the preamp tubes.
    • Lift the covering directly up to avoid metal on glass contact.
    • Gently rock the tube back and forth while lightly pulling upwards.
    • Note the position of the pins.
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    Insert the preamp tubes. This is done in the same fashion as the power tubes except that the pins will have a prominent gap between two pins instead of a nub. Match this gap up with the corresponding gap in the preamp tube socket and gently place it in.
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    Cover the preamp tube with the aluminum case and screw it pack into place.
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    Screw on the protective cage once all of the tubes have been replaced.
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    Plug in the amp and turn only the power switch on. Let it warm up for about 20 minutes. This will allow the amplifier to adjust to the new tubes.
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    Plug in, flip the standby switch, and test out the new tubes.


  • If your tube amp has an adjustable bias, make sure it is at the correct settings for the tubes. If there is any uncertainty, there is no shame in consulting a professional.
  • Take out the tubes first and bring one for comparison while shopping around for tubes.


  • Never touch the tubes with the amp on. These tubes deal with high amounts of heat and electricity.
  • If a tube breaks in your amp, sweep up the glass and use compressed air from a distance to blow excess glass particles out of the amp. Remove the broken tubes using thick rubber gloves for your protection.

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Categories: Maintenance and Repair