I'm new to bass and new to circuits that would sound the way I want bass to sound. My cloning journey, this time, started with the idea of something like an Ampeg B-15, which is like an early '50s Pro with an extra gain stage and a very lossy tone stack. Since my chassis had the right sockets for the latter, I started there. Without a tone stack (just putting a voltage divider there, and another before the PI, so I could hear the amp), and with no NFB, cathode biased, and with all of the preamp triode cathodes unbypassed, it was at its *most* beautiful, but of course the bass was way too strong. I then went through my options for rolling off that bass. I found that I needed steep rolloff to try to get the low notes to behave practically (not *too* touch sensitive), while also allowing more singing on higher notes. I arrived at solid, well-behaved low notes but then the highs got too raspy. To make a long story short: The ouput section is now almost all the way to AA371 (but it still has cathode bias and reduced screen voltage, see '50 RCA Manual). 40Hz is very solid. It is still beautiful in a different way. By setting the volumes right, and by changing the NFB amount, there is versatility too. It's usable. EDIT: Haven't tried the third preamp gain stage yet. But maybe you will recognize this sentiment: I'm haunted by the memory of its earlier tweedish tones, but it wasn't practical. I'll have to get over it, I guess. I never "finished" an amp for 6-string, but I'm determined to finish because I really want to study bass.