![]() ![]() Experiment a little, and see which ones work for you. Also, see if you can find any affordable NOS tubes, or perhaps you can pull some used but functioning examples from old junker radio or hi-fi systems that you find at garage sales and swap meets. Search the internet and read up on what other players consider to be the best current- manufacture tubes coming out today (there's too much detail on that subject to go into here). Try three different makes of 12AX7 or their equivalent in that position, and I'm willing to bet you'll notice a slightly different voice from each. ![]() The first preamp tube position usually affects the tone of that part of the amp the most (read your amp's tube chart or owner's manual to make sure you know how to change tubes safely, and are changing the right tube, and please don't touch any hot tubes! Let them cool down first). Try swapping a few around to see which ones help you to best achieve the tone you are seeking. What does this mean for the guitarist? For one thing, it behooves you to get your hands on as many different makes and types of tubes as you can reasonably afford. ![]() If you're trying distortion and more output-tube distortion, you can also try using a 5751 in the phase inverter position, which is usually the last preamp tube before the output tubes. This 5751 swap is a trick that was used by Stevie Ray Vaughan, for one, to help generate his signature tone, and it has also been employed by plenty of other great blues players. This tip doesn't usually apply to high-gain type tube amps, whose whole raison d'etre is to generate preamp distortion. This generates more output tube distortion, which results in a fatter, fuller tone in many simpler tube amps. Many players think the last thing they want to do is lower the gain of a preamp stage, but in doing so you can often prevent your signal from dirtying up in the preamp, and thereby pass a beefy, full-frequencied signal along to the output stage when the amp is cranked. To lower it even more but retain the same performance characteristics (other than gain) you can use a 12AY7. To lower the gain of a preamp stage a little, you can swap a 5751 into any socket that carries a 12AX7. This can be a great thing if you're looking for a super-fried overdrive tone that's cooking at all stages, but not at all desired if you want more headroom and clarity, or the fatter distortion that's generated in the output stage of the amp when a cleaner preamp signal is driven into clipping at the output tubes (more of which in the next installment).Ĭounter-intuitive though it might sound, armed with the above knowledge regarding preamp tube distortion, many players have learned to create a bigger tone by using lower gain preamp tubes. Drive a 12AX7 hard, however, and it will induce quite a bit of sizzling, slightly fizzy-voiced distortion of its own. They also have a reputation for handling effects pedals very well. Both have higher gain factors than even a 12AX7, but aren't prone to distorting the way that dual-triodes can, and instead pass their fattened-up signal on to the next stage. Both of these pentodes fit the same 9-pin bottle as the dual triodes but require very different circuitry, and are known for their thick, robust sound. Another less frequently seen, but much admired, pentode preamp tube is the 5879, notably used in Gibson's GA-40 Les Paul amp of the late fifties. ![]() The only pentode preamp tube seen with any regularity in amps today is the EF86 (or 6267), which appeared in early Vox amps and has more recently been used in models from Matchless, Dr Z, 65amps, and a few others. Sure, there are some respectable sounding solid-state amps, and digital modeling amps have also made inroads into the market, but ninety-nine out of a hundred serious pros (if not more) continue to use tube amps for both recording and touring, and these little glowing bottles still define the cornerstone tones of rock, blues, and country guitar. Is this just nostalgia, or mere perversity on the part of guitarists? Not in the least: when used to amplify electric guitars, tubes still simply sound better than anything else out there. Bit by bit they have been replaced in all of these functions by other forms of more compact and more stable technology… except in guitar amps, where they maintain their preeminence over all kinds of far more advanced electronics. They glowed their little hearts out in our television sets, car and home radios, hi-fi systems, and guitar amplifiers, and were crucial components in myriad military applications, from radar technology to missile guidance systems and more. Once upon a time, vacuum tubes were used all over the place. ![]()
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