Ageing nicely! The effects of HF must be just right to cause that off cathode break in the arc on every half cycle. With it happening several thousand times a second it must have a stronger effect? I've seen tubes quite heavily banded on HF, even T8!

I was thinking that too. Initially I was under the impression that HF decreased the chance of wear marks but given the atlas f15t8 pink lamp that I have also running on electronic gear (Philips HF matchbox red) is banding at BOTH ends I’m inclined to agree with what you say. Either way, I think by the beginning of spring next year this will be an absolute corker. I’ve started running it 24/7 now, just dimming it at night now it’s got some hours on it.