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How to Replace Tubes in Your Guitar Amp

Date:2020/1/4 17:08:56 Hits:

Whether you’re trying to breathe new life into a tired amp or experimenting with new tones, replacing the tubes in your guitar amp is a fun and easy way to upgrade your amp’s tone. Here’s a guide to replacing tubes along with a few pointers to help you take your tone from lackluster to legendary.

Safety First…

The first thing you need to know about replacing tubes is how to do it safely. It’s no more dangerous than changing a light bulb if you are careful and do it the right way. Make sure you power down the amp, unplug it, and give it adequate time to cool down before you touch anything — tubes can get really hot.

Preamp Tubes

To change preamp tubes, all you’ll need is a screwdriver and a little know-how. On a lot of amps, you will need to remove the back panel; but don’t worry, this will not void your warranty. Nearly all manufacturers expect you to change your own preamp tubes, but check your manual to be sure.

With preamp tubes, you don’t need to worry about things like biasing or using matched pairs as you do with power tubes. As long as your new tube is the same model as what you’re replacing (12AX7, 12AT7, 6SN7, etc.), you’re good. You can even mix and match different brands, and sometimes that’s the surest way to find a tone that is totally your own.

In certain tube amps, the preamp tubes are in a chain, where each tube makes your guitar louder, and louder, and LOUDER. The tube closest to the input jack is the first one in the chain, and it’s a great place to start if you’re experimenting with different tubes. The nuances of that tube are most noticeable because it is re-amplified by each of the subsequent tubes in the chain.

How to Replace Preamp Tubes

After the amp has cooled down, remove the back panel if needed. This is where the screwdriver comes in handy.
If you have any shiny aluminum tube covers, remove them by pushing up and turning counterclockwise.
Grip the base of the tube as close to the chassis as you can. Most tubes are in there pretty tight, so make sure you have a really firm grip.
Gently wiggle the tube from side to side while pulling it away from the chassis. Steady but gentle pressure is the key. Don’t yank!
Make sure the pins are aligned properly* before pushing the tube back in. Use gentle pressure when reinserting the replacement tube as shown in the video below.
*Pro Tip: Pay close attention to the orientation of the pins when removing the tube. Then align the pins correctly before reinserting the replacement tube.

Power Tubes

With power tubes, there are a few extra considerations. First, some manufacturers do not want customers changing power tubes, so make sure to check your manual for warranty rules before you unintentionally void your warranty. Second, most power tube sockets have tabs on the side that hold the tube in place, and you’ll have to hold those tabs down to get the power tube out. The last and most important thing to consider when replacing power tubes is biasing. There’s a lot of voodoo surrounding biasing, but it’s really not as mystical as some people think. Biasing is just the process of adjusting the voltage for each power tube so that they’re both doing approximately the same amount of work.

So how do you know if your amp will need to be re-biased? The best way to know for sure is to read your manual, but in general, most amps with less than 30 watts are cathode biased and won’t need to be re-biased. Amps over 30 watts are usually fixed bias and will need to be re-biased by a professional unless the manual has specific re-biasing instructions.

Rules for Power Tubes

Here are a few rules to keep in mind when changing power tubes:

Read your owner’s manual and pay special attention to anything that mentions your warranty or biasing.
Always replace power tubes in matched pairs (two tubes). If your amp has four or more power tubes, you only need to replace two tubes at a time, but their ratings have to match each other, not necessarily the other pairs. Check out our article What Are “Matched” Power Tubes to learn more.
If your power tubes failed, there’s a good chance your HT fuse blew. Some HT fuses are inside the chassis (especially Marshall and Blackstar models) and are not user-replaceable. Check your manual to be sure.
Rectifier Tubes
A rectifier tube’s only job is to take the alternating current (AC) from the wall outlet and turn it into direct current (DC) for your amp. Because its job is so simple, it will rarely fail. Changing a rectifier tube isn’t as common as changing preamp or power tubes and doesn’t impact your tone as directly. It will, however, indirectly impact your tone by changing the way your amp responds to low frequencies. It’s subtle, but different rectifier tubes can impact the response time of your output transformer and increase/decrease sag, a type of compression-like attenuation.

Rectifier tubes are about the same size as power tubes, and they’re typically closest to the power jack. Most amps only have one rectifier, so you don’t have to worry about biasing or using matched pairs. Even if your amp has more than one rectifier tube, you can use whatever brand you want, just make sure it’s the same model as what you’re replacing.

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