Greetings from MD! I have a really basic question about output tubes: How does one know what the maximum driving voltage should be from the pre-amp? As an example, I am building a mono-block 6L6GC P-P amp, and want to get the max clean output from my tubes. Is there a way to know what the maximum voltage swing I need at the 6L6 grids -- other than by trial and error?

The 300B tube datasheet puts its max output around 8 watts. Why would we want to use a 25 watt rated output transformer for this tube (operated SE)? The 25 watt OTs are so much bigger and heavier than the 10 or 15 watt versions, and most often I'm not listening at full volume anyway. I understand that the original design used the 25watt OTs that were left over from a previous build -- that makes sense. But in a new build, I'd probably spec the 10 or 15watt Edcor OT.