I think you're going to need a hotter iron for your grounds. The brass plate acts as a heat sink and requires a lot of heat to get a good connection. Regarding transformers, take a look at the Weber Proluxe for ideas. I started with one, didn't like it, and changed it to cathode bias. The multi-tap OT allows me to optimize it for 6L6's w/GZ34 or 6V6's w/5Y3. Sounds close to an old cathode bias Pro with the 6L6's for around 25 watts of power. The main differences are the transformers, filter caps and, of course, tubes and a more efficient speaker. It's a really versatile setup.