Why bias tubes

Current going through your heart is bad! What is Amp Bias? No matter the manufacturer, how good the design is, or the quality of the parts used, tubes will eventually wear out. 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.

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. 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.

Left unchecked, we risk not only blowing a tube, but risk damaging other components of the amplifier. There are 3 different types of tube amp bias:. Non-Adjustable Fixed Bias: This category can be the most labour intensive when it comes to setting the correct bias. 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.

This means it is important to buy matched sets of tubes because it is harder to optimize them. For this quick guide we will only be looking at Adjustable Fixed Bias amplifiers, which will be the most common for hi-fi valve-amps. If you are uncertain which you currently own, check the owner's manual. Most manufactures will even include instructions on how to measure and adjust tube bias for their products.

They will more often than not give you the actual range to set the bias to as well. They need changing if you want to keep that great valve tone. So how long do a set of amplifier tubes last? Well, there are quite a few variables, like how hard you play, but 1, hours is about right.

Think car tyres. A set will last longer for a careful driver than for a boy racer! You can buy new tubes here , by the way, before you try to bias tube amplifiers. The big ones. The power valves. Next, your amp will usually have either 2, 4 or 6 output tubes. So if your amp has 4 output tubes, they are simply doubled up to give more power. It means that for a given bias setting, each tube will draw the same bias current. What is Tube Bias? Why Bias Tube Amplifiers?

Setting amplifier bias or adjusting the bias on a tube amp is a confusing subject for the non-technical. You can think of it like the tick-over rate of a car. Too low a bias current and the tubes will last longer but the sound tone will be affected. So we aim to adjust tube bias somewhere in the middle - a compromise between long life and good tone.

So I always bias tube amplifiers smack in the middle of where they should be unless specifically requested otherwise. We have created the definitive "How to Bias Amplifier" Manuals for some of our most popular guitar amplifier valve kits.

Click on any of the links below to purchase that bias manual or scroll down to find out more about amplifier valve biasing. What next? Answer — set the amplifier bias adjustment for that set of tubes in that particular amplifier. This is a variable potentiometer. While there are many in depth and thorough explanations out there, I figured we would strip it back to its simplest form and give an idea of why this is such an important part of a tube amplifier's health and tone.

We will be addressing the two main types of biasing used in guitar tube amplifiers: Cathode bias and Fixed bias. These are two different approaches to the same problem. What is the problem? Let's start with some basics on how a vacuum tube operates. Vacuum tubes are also called electron tubes for a reason!

Every tube has a few parts: the cathode, the plate anode , and the grid. These parts operate inside of a vacuum. The cathode is responsible for the emission of electrons when it is heated. At this point, the hot cathode is producing a bunch of electrons that repel one another in the vacuum. The plate comes in here. The plate carries a positive charge and so attracts the electrons. The electrons go to the plate and become moving current.

Now the grid plays its role: The grid is literally a small mesh of wire that surrounds the cathode without contacting it. By applying voltage to the grid, we can control how many electrons make it through to the plate. This controls the output voltage of our tube and allows us to get a relatively large change in output with a relatively small change in input voltage.

The bias is in relation to the grid.