March 13, 2020. With the influx of vacuum tubes now available for tube amps, you have a myriad of choices when it comes time to replace them. Your tubes may not need replacing; maybe you just want to tweak the sound a little or get a little more crunch out of your amp? How do you decide? If you go on the various forums online you’ll get plenty of opinions but that’s all a matter of personal taste. So here are the basics of what you might want to look for when it comes to replacing your tubes.
No tubes for guitar amps are being made in the US or Britain as before. These had the best quality. This makes tubes like the GE 6550 or Mullard EL-34, installed on Marshall amps through the eighties command high prices – if you can find them. Russian maker SED (Svetlana) made the famous “Winged C” EL-34 – a high quality tube praised by guitarists for years but the company shut down a few years ago. There is a new Russian maker using the Svetlana name but the EL-34 they make does not have the same reputation the former maker had. Tubes now available from brands such as Electro-Harmonix or others using famous British maker names like Mullard and Genelex are made in Russia. Even more confusing – the bulk of OEM tubes amp makers install are re-badged Russian tubes or Chinese. That’s not necessarily a bad thing. After all, if these tubes are good enough for OEM makers, they should be good enough for your amp as well but I have heard of new amps failing in relatively short times due to tube failures. I have also witnessed new amps that had static or hiss that disappeared when the preamp tubes were replaced. JJ tubes are made in Czechoslovakia and are high quality. Shuguang tubes are made in China. First, let’s start with the preamp:
Preamp tubes – these supply the majority of the basic tone shaping of your guitar’s signal. Most of today’s tube amps come with a minimum of three preamp tubes and some, such as the EVH models can come with up to eight. With high gain being all the rage these days, there are preamp tubes that can increase the gain of you amp, albeit at a price! There are many brands to choose from.
If you are running an older amp without all those extra preamp tubes (three in most cases) some players have found that the 12AX7 tubes made in China can increase gain significantly and they are cheap. These tubes have become OEM from some amp makers but tend to sound fizzy and quality control is not as good as those from Russia and Czechoslovakia. Personally, I have found that the Tung-Sol brand – another Russian-made tube with a famous name, is a great choice for older amps. It is a high gain tube that doesn’t sound fizzy. While achieving high gain is popular, some players even prefer a little less gain. In that case they will sometimes use a tube such as a 12AT7 in position V1. This is the same tube type Fender has used for years in the their preamp section – known for clean tones instead of dirt.
If you are new to tube swapping, know that in older amps with three preamp tubes, the third tube (usually third from the left if you are looking at the rear of the chassis, face-up) is called the phase inverter, because that’s what it does. It takes the amplified signal and splits it into two so that the power section can amplify the signal to either a pair or two pairs of power tubes (depending on how many pairs of tubes you have.) Most of the preamp gain is created in the first two preamp tubes (from left) and in particular V1 (the first tube.) You’ll find the tube in V1 has a lot to do with the tone shaping of the sound so what you put there can make a big difference. In newer high-gain amps with more than three preamp tubes, one is always the phase inverter, usually the last from the left. If you buy a complete set of preamp and power tubes from suppliers such as tubesandmore.com, they will match the preamp tube used as the phase inverter to have the same output from both plates of the tube. This is important because if one half of the tube is not pulling its weight, the output to the power amp could be reduced.
In modern high-gain amps such as EVH or others with more than three preamp tubes, you might actually make your amp sound worse by installing high-gain preamp tubes. EVH installs JJ tubes from the factory, which are a high-quality, middle-of-the-road tube gain-wise. They sound very musical and also have a reputation for reliability. I have found that even amps from the early 90’s through today with four preamp tubes or more sound better and more musical by using a tube such as a JJ. These amps supply plenty of gain as they are and modern Metal players tend to use a distortion pedal in front of the amps as well. Putting high gain tubes in on top of this would be overkill.
Another factor to consider as well is whether your amp has an effects loop. Older amps with no effects loop take effects pedals well because they are inherently less gain-y than modern amps. Most of the distortion comes from overdriving the power tubes at full volume. To increase gain (and overdrive the preamp) at lower volume levels you might experiment with a pedal such as the Boss DS-1, Ibanez Tube Screamer TS9 or TS-808 to increase the level of your signal out of your guitar and into your amp before you go adding high-gain preamp tubes. As long as your preamp tubes are in good operating condition you might try this first. Distortion pedals also work well with older amps. Randy Rhoads used an MXR Distortion+ pedal in front of his Marshalls to get his tone.
Amps with effects loops are a better choice in high gain amps because the preamp section is bypassed and the effect signal is introduced into the power section, where your power tubes take the signal, amplify it and send it to your speakers. Users of high-gain amps often will use a noise gate pedal to control the amount of background hiss caused by the preamp section of their amp. Peavey 5150 users know all about the hiss these amps generate because of all the gain in the preamp section. Even Eddie Van Halen uses a noise gate in his pedalboard setup because the amount of gain noise generated by modern amps has to be controlled in order to sound musical.
OK, so what about your power tubes? The power tubes are the large tubes that sit on top of the chassis, usually consisting of two or four tubes. Starting in the late sixties, players discovered that by turning the amp to full volume and overdriving the power tubes, they would get distortion that sounded sweet and musical. It also made themselves and people in front of the audience deaf, at least temporarily.
In the mid-seventies, makers such as Marshall started building amps with master volume controls – enabling the user to set the preamp gain control to overdrive the amp while being able to set the overall volume level with the master volume. This is done by almost all amp manufacturers these days – the preamp supplies more of the distortion in modern high-gain amps. Still, the type of power tube you install can make a difference in the tone of the amp. Tubes such as the 6L6 are used primarily in amps such as Fender, Peavey and EVH. They have a different sound when pushed hard, than the typical EL-34 tube used in Marshall and amps of a similar lineage (Hiwatt, Laney.) 6L6s tend to sound a little harsh, in my opinion when pushed hard because they were designed initially for cleaner sounding amps like Fenders so it takes a little more to push them into overdrive. One exception I’ve heard is the EVH Stealth series of amps that use 6L6s. Some tweaking was done by Van Halen with Fender and these amps sounded warmer and less harsh than some earlier models.
EL-34 tubes distort sooner, requiring less gain to overdrive them, sounding less harsh but more “British” and a bit different than Fender-style amps. As a result of distorting sooner, British-style amps with EL-34s don’t sound as clean as Fender types though they have made improvements through tweaking and multi-channel setups. Other power tubes such as KT66s, KT88s, 6550s and 5881s have their own characteristics as well. If you were to try and substitute these tubes for your EL-34s or 6L6s it would require re-biasing the amp in order to set the correct level of bias for the power tubes. Often, this would require changing some components of your amp as well. This is better left to an amp tech that has performed these modifications previously. I would recommend you try the same type of tube from different manufacturers before you go changing tube types.
To sum things up:
Try and boost the signal coming from your guitar first if you want higher gain before you go swapping tubes. As stated above, the Boss Super Overdrive SD-1 ($50), Ibanez Tube Screamer (TS-9 or TS-808, $99, $179) or similar overdrive pedal will boost the signal, letting the amp create the distortion and giving you a more organic amp tone than a distortion pedal. The SD-1 is cheap but has been around for over 30 years, sounds great and doesn’t color the sound of the amp.
Non-Master and Master volume amps from the sixties through the eighties – for higher gain try Tung Sol 12AX7 tubes in the preamp section and EL-34 in the power section if so equipped. These are great sounding, musical tubes that are high quality and not expensive. You’re not going to get heavy distortion but it will sound crunchier. JJ preamp tubes will sound good as well with a bit less gain. Get a matched pair of El-34s and 12AX7s with a matched phase inverter. If you want to try an even higher gain preamp tube try the Chinese-made 12AX7. If you run 6550s there are several good reissues out there from Tung-Sol, JJ and TAD. The same applies for 6L6, KT88, KT66 and 5881.
You can buy a sampler set of 10 12AX7 preamp tubes from tubesandmore.com here. This is a good way to find the best sounding preamp tube that suits you. It’s expensive ($139) but it could be worth it to you. They also sell a 5-tube set that doesn’t include the Chinese 12AX7.
High gain amps from the early nineties to today – concentrate on high quality tubes. JJ, Mullard, Tung-Sol and TAD (Tube Amp Doctor) are some with good reputations for sound and quality. Don’t go for high gain in the preamp as these will contribute to the fizziness of the amp. A good place to research the different brands of tubes is tubesandmore.com.
If you’re using a distortion pedal in front, don’t go high gain in the preamp. Use the effects loop if your amp has it and look for a tube that claims to give the type of bottom-end response you want. If you scoop the mids of you amp, look for a tube that gives clarity to your sound.
In the end, the best tubes for your amp come down to how they sound to you. Whether you play blues, Rock, Metal, Jazz, Country or a combination of all of these, your ears have the final say. Have fun!
Remember to turn your amp off before changing any tubes. Allow a few minutes for the tubes to cool down before removing them. Make sure the amp is grounded to prevent any possible shock. Only touch the amp chassis with ONE hand, keep the other in your pocket. Remove all jewelry from your hand before touching the amp. If your amp uses a three-pin plug, leave it plugged in with the power off and this will ground the amp.
In another article, I’ll tell you some ways to troubleshoot your amp if it doesn’t sound as good as it used to or if it isn’t working at all!
Have you found a brand of tube that sounds good to you? Tell us about it.