![]() ![]() The AC4 uses two 32 μF caps and one 8 μF cap. Filter caps typically have values in the range of 8–50 μF, sometimes higher. What emerges is actually a ripple-like DC voltage, so the filter capacitors help reduce the ripple by storing and releasing high voltages. The rectifier tube does a good but not perfect job. The rectifier tube's purpose is to convert the AC voltage (a sine wave) into a constant DC voltage to power the tubes. These are why you don't mess around inside your amp unless you know how to do so safely. Unlike batteries for household items like flashlights and smoke detectors, they hold potentially lethal voltages. There are three types of capacitors in a guitar amp-filter, bypass, and signal-and their values are measured in microfarads, which are designated by the symbol μF.įilter capacitors are large metal cylinders that, like batteries, hold a charge-even long after the amp has been unplugged. In some schematics, one of the lines may be curved. Enough electrons will travel from the EL84's plate to the output transformer to drive the speaker.Ĭapacitors are shown in the schematic as two parallel lines perpendicular to the wiring. At the EL84, a similar electron flow takes place, but this time it's more powerful. 047μF signal capacitor, and through the volume potentiometer to the grid of the EL84. The electrons released by the guitar signal flow from ground to the EL86 cathode, then to the plate, through a. ![]() A bypass capacitor is put in parallel with the resistor to increase gain and allow AC electrons to effortlessly get through. However, the cathode resistor alone would also affect electron flow when the guitar is played. When the guitar signal reaches the grid, the electrons then flow. This creates the small DC voltage on their cathodes to prevent the electrons from flowing. The cathodes of the EF86 and the EL84 each have a resistor attached to ground. (In the AC4 schematic, the ground connections look like upside-down Christmas trees.) Electrons flowing through a tube originate from ground. In practice, ground in a guitar amp means a connection to the chassis. We all know your guitar's signal comes from your pickups, but to understand the amplified signal, let's start at electrical ground. That rush of electrons from the cathode to the plate mirrors the signal from the guitar, amplifying its signal many times over. And when you position the grid close to the cathode and connect the grid to the relatively tiny voltages coming from your guitar pickups, something interesting happens: The tiny signal unleashes a flood of electrons, allowing them to fly freely to the plate. When you add a third element-the grid-between the two, you can control the flow of electrons. If you place these two elements in a vacuum and power them up, electrons will fly relentlessly toward the plate. To the highly positive plate, the cathode's slight positive charge still makes the cathode seem negative (we'll talk more about this slight positive charge later). The plate carries a high positive charge that's ready to pull those negative electrons toward it. Surrounding the cathode is the anode-although in the guitar universe we typically call it the plate. It's especially ready if it's been heated. ![]() It carries just a slight positive charge, and it's ready to release a gazillion electrons. Picture this: In the center of a tube's glass envelope is a cathode. In guitar amps, we're not that interested in displaying images with our tubes, but we're still very interested in controlling those electrons-and we can use a guitar to do it. ![]()
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