>it takes 20 hours to discover what you could have learned in 10 hours on the breadboard, or 1 hour plagiarizing tube-manuals and competing products.
...or 40 hours searching for the right PRR post.
I've no doubt learned more from reading PRR than from everything else combined. My #1 source of brain candy. I really like TubeCad. The only problem I've had with it is that it tends to forget scenarios when I save more than 2 at a time. I have verified it's results time and again on my breadboard. I treat TubeCad like my classroom and my breadboard like lab time. All of this has helped me move beyond blindly sticking various Leo Fender circuits together like leggos.
IMO, you need a mix of stealing circuits, guru advice, software, and breadboarding. My last project was a preamp/headphone amp. I stole from Morgan Jones, was advised by PRR, explored in TubeCad, and experimented on my breadboard until my heart was content. The experiment looked like this:
and the prototype looks like this:
The finished prototype worked right away. My only issue was a milling error. Someday I'll learn to read a tape measure all on my own.
I'm gonna stay +1 on the TubeCad. It's by no means the sole solution to the learning experience, but much can be gained from clicking around it's variables.