I recently built a 5F2A with a few tweaks for myself and found that it's a really great amp for home practice and low volume jams. SO much better than trying to control a big amp at home. I let a friend borrow it for a few days and he convinced me to make him one. Anyway, the original has a Weber Champ/Princeton OT (22905M). For my buddy's amp, I wanted to try the Classictone version (18030 I believe). The rest of the components on both amps are identical. While I know that every component has tolerance and the whole can vary in noticeable ways, these two amps are DRASTICALLY different. I looked over both amps for days trying to figure out why such a different response between the two. tone controls, partial shorts to ground, resistor values, tubes, caps, etc. When I couldn't find it, I decided to swap the Classictone for a Weber and BAM, the two were much more in line. Point it here is how drastic the tone and feel of an amp can change using different output transformers. I know they are important to the tone of an amp but never witnessed it first hand.