When you bought your tube amplifier a major factor was probably how good it sounded! You worked it hard for a long time and made a lot of great music with it, and then one day you noticed it just didn’t seem as awesome as you remembered it sounding. Or perhaps you were playing and one of the tubes died, leaving you wondering what it would take to bring it back to life? Sooner or later, every tube amplifier aficionado will have to face the confusing task of choosing replacement tubes for their amp. Let’s look at how you can sort through the hype, get the great sounding tubes you need and avoid paying more than you have to for them.
From groovy sounding brand names to ones that sound like rare jewels and precious metals, the tube marketing industry loves to sell us their quality. But are those expensive boutique brands that sell tubes from the same factory worth the extra money? Well, it depends. In order to make the right choice for your situation you’ll need to know a little bit about how tubes work, and a little bit about the tube industry. Let’s take a look inside the world of tubes.
Choosing the right preamp tube is a subject all of its own. They do not have to be the same brand as your power tubes, nor even from one to the next. Since they are self-biasing in the circuit you don’t need them matched. With basic electronic safety skills most guitarists can learn to change their own preamp tubes without a technician. The fancy tube companies many times are not making the tubes, but they are doing secondary testing and separating the tubes into more categories for gain, output, microphonics and other characteristics. Different brands direct from the factory distributor will have different characteristics of gain and output also. You can save some money and buy a few different models and manufacturers to try out through the factory distributor. Then if you want to compare to a “higher end” tube you can try one of them. Carvin Audio sells the same tubes that come stock in the amplifiers, so if you want the same tone replace your Carvin amp with the same tubes. Note: Carvin Audio uses two different pre amp tubes, the 12AX7C which is a high gain tight low end preamp tube and the 12AX7JJ tube, which is a lower gain more broken up preamp tube at high gain settings.
Now what is important for your power tubes is that they are reasonably well-matched, which is an industry term for selecting tubes in sets that draw the same amount of current under a given bias voltage. This matters because most amp designs do not have individual tube bias adjustments and the amp design relies upon both sides of the circuit amplifying part of the signal accurately. A mismatch will create distortion (of a type most musicians do not find appealing). While the fancy brands offer matched tubes, the factory distributors do too and sell them for a lot less. Either way you will still need your amp adjusted to the optimum bias voltage by a qualified technician.
So what advantage do the boutique tube companies offer? You can order matched tubes from the factory distributor, but they don’t distinguish between how much current those matched sets draw in the circuit (which is why the tech has to bias it). So the next set of power tubes you order from the factory may have an entirely different draw, and you’ll need to pay your tech to bias your amp all over again. Boutique distributors often sort their tubes by current draw (or “hardness”) and mark it on the package so you can ask for the same ones next time and put them straight in the amp without a tech adjustment. This can be convenient for the hobbyist who can afford it and an important advantage to a working musician that might need to replace damaged tubes on the road without test equipment or a technician.
There will always be lots of mystique and hype around tubes and tube products, but much of it is just that, hype. This does not mean that a particular company does not have a great product or new testing technique, but you will just have to dig in and do the research. For those just looking for a new set of tubes to get your amp back up and running, look into the tubes the amp came with and start from there. If you want the same sound, get the same or very similar tubes. If you want to experiment, try other brands or styles of the same type of tube.
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Even if you’ve matched your bass head and cab properly impedance wise and set your amp for clean sound, sending simply too much power to your bass cab can result in blown speakers. This often happens when you are using a rig you are unfamiliar with, as we tend to know the limitations of our own equipment and have chosen that setup for a reason. Borrowing another bassist’s amp or using a backline rig only to blow it up is definitely not a great feeling.