![]() Make sure your supplier allows you to request the same 'hardness' or current-rating as the last set you purchased. Do your research: some wholesale tube importers sell tubes that are 'matched' within the set but not from one set to the next. So it is up to you to decide the best approach for your needs. Of course just like your technician, the boutique tube companies charge you for matching the tubes. Just keep an extra set of matched tubes on hand for quick replacement without re-biasing. This can be an advantage if you're on the road or at a critical show and experience an unexpected power tube failure. But the theory is that the next time you need tubes you can order the same set from the tube company and they will bias properly in your amp without changing the adjustment. The first time you buy these current-matched tubes you still have to get your amp biased by a tech. Usually they are labeled into categories rated 'hard' or 'soft,' or sometimes identified by current ratings. Next the tubes are sorted into bins of tubes that draw the same current. They take all the stock tubes and put them in a test circuit to measure the amount of current they draw. ![]() The boutique tube companies take a different approach. When they're finished you have to pay them for their time. If you buy regular tubes and take them to your technician to get the amp biased, they put them in the circuit and adjust the amp until the tubes draw the proper current. What about these tube companies that say if you use their tubes you won't have to re-bias your amp? You wouldn't enter a stock car race without getting your motor tuned up properly for similar reasons. If the bias is too far the other way they won't draw enough to operate efficiently and they won't sound right. If the bias is incorrect your new tubes might draw too much current and burn out. Each set of tubes you put into your amp responds differently to the bias voltage. Setting that bias voltage is what amp technicians commonly refer to as 'biasing your amp.'īiasing is important because there is a lot of variation from one tube to the next. But since power tubes are a consumable part that needs to be replaced regularly, we need a way to adjust the bias voltage that governs how much current the tube draws. Most components in a guitar amplifier don't need bias adjustment the circuit is designed to provide the correct voltage in the right places. It could also provide just enough information to get through a tube failure in a pinch.Įlectronic components like tubes in circuits need specific voltages at their terminals in order to work properly. ![]() Still, having a grasp of the general concept can give you more options in fine-tuning your amp's performance. You could play a tube amp all your life without knowing or caring about the reasons, especially if you have a great tech to maintain it. ![]() But the reasons why always seem just a bit mysterious because the related folklore among musicians clouds the issue. For example, these days most players with tube amps know that we have to get our power tubes biased when we replace them. Sometimes we learn to do something without understanding why it is important.
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