How to Know When to Change Preamp Tubes

Written by andy osborne
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Preamp tubes--often referred to as vacuum tubes--create a rich, warm amplified sound that is sought after by many music lovers in the age of newer, solid-state amplifier technology. However, since preamp tubes are made of glass, they are not as durable or long-lasting as their solid-state preamp counterparts, and need to be replaced periodically. Knowing the signs of dying preamp tubes is crucial in replacing them to keep your preamp delivering the sound you want

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Things you need

  • Preamp with tubes
  • Speakers or speaker cabinet
  • Speaker cables
  • Power source

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  1. 1

    Track how often you use your preamp, as well as how long the current preamp tubes have been installed in the unit. According to Matthew Toledo of Athens Musician Network, the lifespan on average of a preamp tube is roughly three to four years if you use your preamp three to four times a week.

  2. 2

    Plug in your preamp, connect it to your speakers or speaker cabinet, and turn the unit on. Let your preamp warm up for at least two minutes, to allow the preamp tubes to heat up to their running temperature. This warm-up period is essential in giving you a more accurate indication of the tubes' performance than if you try them immediately after turning on your preamp.

  3. 3

    Play music through your preamp and speakers, and listen for the sound of something called microphony, advises You can't miss this high-pitched, whistling sound, which will emerge from your speakers when your preamp tubes are getting old and need to be replaced.

  4. 4

    Listen to the volume levels produced by your preamp. When preamp tubes are on the way out, they will produce less volume. Also, keep an ear out for a low rumbling sound that becomes more apparent as you increase the volume level on your preamp--another symptom of preamp tubes that needs to be replaced.

  5. 5

    Turn off your preamp, unplug the unit and allow it to cool down for several minutes after you check for microphony and volume problems. Let it cool down longer if you've been playing through it for hours--make sure that your preamp tubes are not radiating any heat before you remove them. Examine your preamp tubes for visual signs that indicate they need replacing--cracks, broken filaments or scorch marks.

  6. 6

    Check the fuses in your preamp. If one or more of your fuses are blown, a bad preamp tube is the likely culprit, says Toledo. As preamp tubes age, they lose power efficiency and are forced to pull more power in order to warm up--and blown amp fuses are a key sign to watch for. Keep in mind that if you continue to use your preamp with a blown fuse, your vacuum preamp tubes may pop as their filaments overheat.

Tips and warnings

  • Never turn on your preamp without first connecting it to speakers or a speaker cabinet--this can cause preamp tubes to overheat, creating a potential fire hazard, as well as a quick demise for your tubes.

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