Tubes are produced in batches, fairly large batches at that. All you will find are values for Total Harmonic Distortion (THD) at different operating voltages and current levels. You will never find mention of breakup or onset of distortion. All of that good stuff happens after production. You will never find a tube manufactured as clean or dirty sounding. They are essentially interchangeable but provide different amplification factors. Some tubes are created to intentionally have different gain characteristics, but this is typically found in small tubes like dual triodes, such as the 12AY7 and 12AX7. As single ended or push-pull pairs, the tubes will react differently, and the manufacturers provide guidance on how to use their devices. They also specify typical values for these criteria when the tube is operated in different modes. They specify maximum levels for voltage, current, capacitance and output power. The electrical properties are more diverse. Things like the height, width and type of base are quite common. There are a lot of numbers that describe the tube’s properties in terms of dimension and electrical ratings. Let’s look at a typical specification sheet for an output tube. The physical structure of a tube and the materials used to make it, have a big impact on the success or failure of meeting those designed properties. Vacuum tubes are mass produced devices that have electrical and mechanical design properties. Are tubes designed to distort? Can they be designed to distort? An interesting idea, and perhaps valid, but not something that I had thought about when reviewing tubes or building amplifiers. At least 1 company advertises tubes as being matched based on breakup characteristics. It seems that there are people looking to get early breakup in their guitar amps and they want to buy tubes that will give it to them. I recently had a discussion with my friends at. Metal took off and heavy distortion was here to stay. Mesa Boogie was the true champion of this cause and in the 1970’s and 1980’s many people took their Fender amps to the shop for modifications to try and get the Boogie sound. The main idea was to create the breakup before the output section and use the output to amplify the already distorted signal. Engineers developed effect pedals that would generate thick distortion and amp designs shifted to having a master volume and multiple, cascading gain sections. People wanted their amps to breakup at lower volumes, and more severely than they had in the past. In the 1970’s, amplifier design started to change. Most of this glorious tone was delivered by pushing those amps hard and causing the output tubes to distort, or breakup. Rock music was at one time considered nasty and aggressive, so the sound of overdriven amps was the perfect marriage. It just so happens that a lot of people like this sound. When treated this way, tubes start to work outside their designed parameters, compression occurs, harmonic frequencies are generated and the tone gets fat and aggressive. systems weren’t available so amplifiers were pushed to the breaking point. Rock and Roll wasn’t a thing and distortion wasn’t cool yet.Īs musical styles evolved from the 1950’s onward, the sound of overdriven electric guitar became a big part of the musical landscape. They just wanted to be heard by the audience. And you know what? They didn’t want distortion. These old amp designs stretch far into the past, to the early days of amplified instruments. If you have an old-school tube amp without a master volume, then you know the only way to get breakup is by turning up the volume and moving some air.
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