If you would like to hear some of the greatest tubes, there are some interesting audio types that are electrically equivalent enough to be accepted for intercha

If you would like to hear some of the greatest tubes, there are some interesting audio types that are electrically equivalent enough to be accepted for interchange in properly designed power amplifiers. Most traditional tube amps were designed with only the performance of a single particular tube type in mind. To keep distortion to a minimum, this can be a baseline requirement for audiophile performance when replacing tubes. But with guitar amplifiers different amounts of distortion are desired or not at different times. So these guitar circuits can be made more amenable to the limited variety of electrically suitable US and overseas choices having compatible pinouts. Something like this: http://www.kometamps.com/products/amplifiers/komet-60 http://www.kometamps.com/products/amplifiers/komet-60 where it can accept any of the US-style 6L6, 6CA7, 5881, or 7581 or the European-style EL34, KT77, or KT66 These all have compatible pinouts but they are not all supposed to be the same. Each tube type had various vintage and some current manufacturers using components of differering material and geometry to achieve characteristic performance for that type according to its data sheet. All of these types fall into a close enough ballpark where a musician can try different types according to taste in some amps, even if this would not be the traditional approach. For guitar amplifiers the incoming signals often drive these tubes beyond the linear range shown on the data sheets anyway. And at high volumes the differences in tubes' internal construction can be heard even more so in the suitcase-style amps where the tubes are right there by the speakers. Plus there's the smaller preamp tubes, so many amps use nothing but 12AX7's in the preamp but there's a whole lot of different guts inside different 12AX7's over the decades.