I've used a number of different types of tubes in my F2B over the years. Most recently, they've had 5751s for their clean and sturdy tone. I just got my McIntosh MC2015 rebuilt and the tech does a lot of tube amp stuff, hifi and instrument. I asked him about good tubes for the F2B, and he reached into his wall of tubes and pulled out a couple of white boxes. "Here, try these." "How much" "Happy birthday!" (It's not my birthday, but who am I to dispute). They are a pair of Amperex Bugle Boy tubes. I never really bought into the idea that some tubes have magic that others don't but these are really amazing. The level of clarity over previous tubes is instantly obvious. I'm a fan! And given the way they made tubes back then, they should last most of the rest of my life.
An unexpected gift. The best kind.
