There is a great debate about that Norman. I don't agree with that. I think that heating the filament and having the oxide coating burn off constantly is a greater issue than the current inrush (not an issue in a current limited supply) and thermal shock issues. It's preference, but there is no definitive science on about it. Frankly, if you are using old tubes, I wouldn't worry much either way. Most tubes made before the 80s will outlive you unless there was a production flaw, you run the heck out of them (which the Lampi does not do), a device fails with the tube in it (light show) or they get dropped. I have had the same quad of 6L6 derivative tubes in an amp that runs the tar out of them for years. Still no sign of failure and they test 75%+. They were made in 1944 and, trust me, there is no babying like the lampi does to its tubes.