The "weird variables" may have to do with the various changes in manufacturing over the years. "Tube screamer" refers to at least 10 different units. Maxon, Iba

The "weird variables" may have to do with the various changes in manufacturing over the years. "Tube screamer" refers to at least 10 different units. Maxon, Ibanez, TS9, TS808, and zillions of clones.