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.