Mesa Boggie (the original) was a sufficient modification on the Fender circuit not to be a patent infringement(if Fender even had a patent on their generic tube circuit). The basic tube amp circuit existed well before Fender was a company, and is probably not patentable at any stage in the game. So the mods that any company makes on the basic tube circuit are probably not a patent infringement of any sort, against anybody. Mesa (I know) does have some patented circuits now, and Fender probably does too now. For example, in 1998, Mesa patented their "solo boost" design that was used on the Nomad (and probably other amps thereafter). So if some other company were to actually COPY that circuit, it might well be a patent infringement (and I would not be in favor of that). But if some other company developed a different design of a solo boost, it would not be an infringement, and would just be free enterprise and competition (which I think is good).
But there is a lot of latitude in the generic tube amp circuit that is not patentable. It grew out of radios that existed 100 years ago. "Improvements" on generic, unpatentable designs are not patent infringements against anybody.
I used to own a Fender amp. I now own a Mesa and a Bulgera amp. I know enough about patent law to know that nothing about the Mesa violates any concept that Fender could have ever patented. These amps are too different. After reading up on Matchless amps, I can well see that my Bulgera V22 is WAY too different from anything that Matchless offers to be in violation of anything that Matchless could have under patent.
Patent law is a very difficult and technical subject, about which I know something but am not an expert. Merely building a tube amp does not violate any patent of Fender. Merely building a tube amp with high gain stages does not violate any patent of Mesa. And if Matchless had any patents on its amp design, the Bulgera V22 would violate none of them, because it is too basically different. Basic, generic tube amp design is in the "public domain" and unpatentable. Mere improvements or modifications on this design are unpatentable, and are not infringement on anybody's patent. A few additions to generic tube amp design have been deemed to be a sufficiently significantly departure from basic and generic tube amps to be patentable, such as Mesa's "solo boost" circuit. But even then, other amp makers have found a way to design significantly different ways to add solo boost so as to avoid infringement on Mesa's patent.
At this point, I am rather sure that my Bulgera V22 is not in violation of anybody's patent. And, again, I have not seen or played on a Magician amp so I don't know if it violates anybody's patent or not. I hope not, because I hate patent infringement, but love competition and innovative design therein.
