Not very familiar with the Rogue... The BC-21 is a very simple straight-forward design, so you are listening to the tube in many respects.. I have had the best results with the Tung-Sol VT-231, Ken-Rad VT-231 and the Sylvania 6SN7W. The stock Philips tube are pretty good for a new tube. I believe Rogue uses a similar or same tube in the Magnum..
Gilbert will still build you a new 6SN7 BC-21. You will just have to buy your own tubes. One of the main reasons he stopped making the BC-21 was a poor supply of new tubes that meet with his criteria for quality.
You could also try posting something in the forum at the Blue Circle website.
The upgrades Salsumma mentions are very good. If your budget allows, you could also ask Gilbert and Angela (and myself) about the Blue Circle "Sugarbrie" preamp which is a Dual-Mono 6SN7 design like the BC3000 and Galatea, with a similar power supply..
Gilbert will still build you a new 6SN7 BC-21. You will just have to buy your own tubes. One of the main reasons he stopped making the BC-21 was a poor supply of new tubes that meet with his criteria for quality.
You could also try posting something in the forum at the Blue Circle website.
The upgrades Salsumma mentions are very good. If your budget allows, you could also ask Gilbert and Angela (and myself) about the Blue Circle "Sugarbrie" preamp which is a Dual-Mono 6SN7 design like the BC3000 and Galatea, with a similar power supply..