Tube amp guitar12/30/2023 This allows each tube to be pushed further, into higher amplification, during the time it's conducting. Unlike in a class A amp, each tube is at work only half the time. One conducts the first 180 degrees of the wave, and the other conducts the second. In a class B amp, two power tubes share the sine wave. Because the transfer of the signal from one tube to the other is never perfect, it creates crossover distortion. In a class B amp, each tube carries exactly half of the signal. To help understand how all that power turns into hardly any sound, we'll discuss EL84 tubes-although any power tube could serve as an example, since all are guided by the same physics. More than 99 percent of the incoming power ends up as heat. A tube amp is therefore far less efficient than you might guess. Power-wise, the speaker operates mostly as a heat sink. Power transformers get warm, the pilot light and heating filaments within the tubes suck up a lot of juice-the preamp tubes and power tubes are approximately only 50 percent efficient- and there's heat being produced by the output transformer. Here's a question that Steven Fryette, of Fryette Amplification and Sound City Amps, is frequently asked: "How is this a 30-watt amp when it says 100 watts on the back?" The short answer: An amplifier is filled with components that consume power that never gets to the speaker. It's more of a space heater that produces sound. When discussing power and watts, keep in mind that your tube amp isn't primarily functioning as a guitar amplifier. Apparently when Vox printed that panel in 1960, they were just kidding. Furthermore, the 225 and 245 selections were both connected to the 245 terminal. That setting connects to the power transformer's 105 volt terminal. Despite the control panel's graphics, the amp never had a 115 volt option. While there were no markings on my AC15's power transformer, chassis photos of two exact same amps and transformers showed the power transformer input terminals labeled as 105, 145 (not connected, like on mine), 160, 205 and 245. A week of deep Google searches and an eventual exclamation of "Thank you online discussion boards!" uncovered the problem. A few Variac voltage experiments over the next few days, along with some obsessively created Excel calculations and charts, verified that a wall voltage of 105 would be more appropriate. Its original Mullard EL84 power tubes were being overloaded at almost 17 watts, while 12 watts is the designated maximum and 14 watts would be pushing my luck. However, the readings I got when checking the internal voltages were sky high. wall voltage to be a few volts higher than its nominal 120, but still within reason for powering the amp at the 115 setting. The AC15's international voltage selector on the far right of the control panel has settings for 115, 160, 205, 225 and 245 volts. That meant replacing the electrolytic capacitors before daring to turn it on, since they have a life span. (full disclosure: many years ago) and finally got around to restoring. I recently had a revelation about a beautiful, fawn-Tolex-covered, circa 1960 Vox AC15 that I bought from a dealer in the U.K.
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