I recently got a new Blues Jr IV. I've had a few through the years. After going through a bunch of amps I decided to go back to the old classic as it's always been the most tonally reliable for what I go for. Knowing the drill on this amp, I immediately swapped out the speaker for a Cannabis Rex (which I am very familiar with and prefer), the power tubes for JJs and the 12ax7s for russian Electro Harmonix. I plug it in to mess around, and holy cow is it ice picky. Like.. 20% more harsh top end than I've ever had with one of these. And especially with the Cannabis.. that's a surprise. I had to turn the treble down to 4 before it wasn't harsh, but then it's lacking all the top end too. The only thing I haven't used before is the Russian 12ax7s. But I got those because they -supposedly- affect a good bottom and round top end to the tone. Right now I am playing music through the amp to break it in for a while. But I'm really surprised how harsh the top end is. Not sizzly, not chimey, harsh. If I push the fat boost, which I usually love and prefer, it's only worse. Before I assume it must be the ehx 12ax7s is there something I might be missing here?