This means it is important to buy matched sets of tubes because it is harder to optimize them.įor this quick guide we will only be looking at Adjustable Fixed Bias amplifiers, which will be the most common for hi-fi valve-amps.
They use a fixed resistor soldered into the amp to set the bias and for the most part, can be used with a wide variety of tubes that have the same operating characteristics as the ones being replaced. Non-Adjustable Fixed Bias: This category can be the most labour intensive when it comes to setting the correct bias. Enjoy your music and if you blow a tube, just replace it with a matching one and you’re ready to go!Īdjustable Fixed Bias: Amps that fall into this category include an internal or external potentiometer/knob that with some basic knowledge, can be adjusted with ease to set the bias. Self Biasing/Cathode Bias: As the name suggests, these amplifiers are essentially ‘plug-and-play’ and will not need to be tinkered with if tubes are being replaced. There are 3 different types of tube amp bias: Left unchecked, we risk not only blowing a tube, but risk damaging other components of the amplifier. Simply put, we want to make sure all the tubes are working (roughly) at the same strength and thus have the appropriate amount of current flowing through them. If set too high (often referred to as running hot) it can sound harsher, less accurate, and can greatly reduce the lifespan of the tube. If the bias is set too low (often referred to as running cold) the amp can sound thinner and less dynamic, and generally won’t be performing at its best. Without getting into too much detail, changing the bias controls the amount of current that flows through the vacuum tubes of your amplifier, with each having an optimum setting. They also don’t wear at even rates meaning eventually some tubes will be working harder than others. No matter the manufacturer, how good the design is, or the quality of the parts used, tubes will eventually wear out.
When prodding an amp keep one hand at your side - you don’t want to complete a circuit with your arms. Wear short sleeves and remove any rings or jewelry. Make sure the amp is unplugged before changing tubes or parts. Even when unplugged, the amplifiers capacitors are charged with enough high voltage to be fatal! Most is common sense but if you are ever uncertain, seek the help of a professional. We can’t stress this enough - make sure proper care is taken whenever operating or making adjustments to your tube amplifier. Whether you currently own or are considering exploring the wonderful world of tube amplifiers, there are a few things you should know to make sure you get as much enjoyment and life out of your valve gear as possible! I am of course referring to tube bias - an important part of amp care that will increase tube life and the overall sonic performance of your stereo.
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