![]() ![]() In order to set the correct value of the quiescent current on an amplifier, a certain amount of experience and technical skills are required. So the setting is particularly important with these amps. Here, the value is the same for all electron tubes and must be hit as accurately as possible during a valve change. The fixed bias is present in classic Class A or Class AB push-pull amplifiers. Here it’s important to know the correct values and to hit them as accurately as possible using matched electron tubes. ![]() Guitar amplifiers which are equipped with a fast bias operate with constant quiescent currents, and the calibration of electron valves cannot be performed. But even with amps which have an autobias, attention should be paid to the most uniform value of the electron tubes used. A tube change is particularly quick and easy with autobias. The amplifier is “intelligently” designed and regulates the bias of the power amplifier tubes or the power amplifier valve independently. There are basically three different variants which have to be observed during the bias check: Autobias Manufacturers use different calibration methods for the layout of their amps, which perform an automatic calibration or require the bias to be set manually. ![]() Whether the quiescent current has to be adjusted when replacing a guitar amplifier’s tubes depends on the technical design of the respective device. In the following part, we explain which options are available for this for amps. In order to optimally adjust the amplifier and get the best performance out of the equipment, the quiescent currents of the individual electron tubes should be matched to each other during the bias check. Due to the design of electron valves, different values and deviations of up to 20% can occur – even with the same valve type. The bias refers to the amount of electric current which passes through the tube while it’s underutilised. Whenever an electron tube in an amplifier is not operated under full load, but is supplied with less energy, the bias has a considerable influence on performance and, at the end of the chain, also on the tone of the tube. There are still a lot of uncertainties, especially when it comes to tube replacement – but at the latest, when we talk about adjusting the bias, is where most musicians draw the line.Īmplifier bias adjustment – what is it actually? In addition to costs, heat generation and weight, the high maintenance level of tube amplifiers also plays a role. ![]() Unfortunately, this organic, lively sound quality is not without its drawbacks. No other amplifier technology delivers such an organic and “tangible” sound as electron tubes. Tube amplifiers are still the undisputed number 1 when it comes to sound quality and feeling. Analogue technology needs analogue treatment In our article on bias adjustment, we try to explain the technical background and functions of quiescent current, give tips on the correct settings and reveal which amplifiers need to be set in the first place. « When is a bias adjustment of the quiescent current required? » ![]()
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