This is fantastic - the group is relatively quiet for weeks, and suddenly we get this brilliant thread on a most interesting subject! :) So, some thoughts... Chris might want to approach ebay seller electroware regarding 6909 supplies. He has sold quite a few of them from some kind of bulk supply box - they seem to be NOS, but not boxed, and usually go at reasonable prices. He is also aware of the problem of duds with this tube type and usually offers them with a guarantee not to be DOA - my guess is he's doing a simple striking test. With regard to the gas fills in high speed tubes with orange glows, I have not come across any definitive statement tying a particular mix to a tube model. There is literature discussion of a Ne/H/Ar mix - my guess is it's something like that here, but as Mike said, we need a spectrometer to be confident. Hydrogen seems to be a common feature of high speed dekatrons as it reduces the deionisation time of the gas and allows higher frequency stepping - the fastest tubes are pure hydrogen (blueish glow). A couple of observations on orange high-speed dekatrons (by which I mean anything quicker than 4kpps). First, most show a blue/purple glow associated with the anode. You can just make it out round the rim of the anode disc on the 6910 photo which Mike posted, but it's most clearly seen on auxiliary anode tubes (GSA10G, Z572S). Here's one of mine in action - the blue glow is around the auxiliary anode pins. Secondly, although many of these high-speed tubes have one or even two standard D shaped getters, I have never ever seen the standard mirror of flashed barium on the wall of the tube. Anyone got any experience that runs counter to this? From this observation I've been thinking in a couple of directions. First - perhaps the gettering material used in these tubes isn't that standard stuff, even though the getter units look absolutely the same as on neon tubes. Quite possible. Second option, the tubes as manufactured did have standard getter flashes, and over time these have been consumed and lost. For a number of reasons, I'm currently leaning towards the second explanation. Not least because it ties up with the observation that all these tubes have a significant dead rate now, regardless of manufacturer or model - something you might expect if there was some process at work which was slowly (over decades) exhausting the getters and then poisoning the tube. I don't think we're looking at gas leakage in the sense of the envelope or pin seals failing though. More likely it's chemistry going on - hydrogen reacting with something in the tube. To Nick's question about Raytheon 6910/6909 and whether they were any better than Sylvania's flavour... A couple of years back I did think the Raytheons were better, but looking at my collection now the numbers seem to have evened out. They're both running about 50% dead :(. The Mullard Z505S is the biggest nightmare though - a large majority of them seem to be dead or dying. Good job Chris' lovely counter hasn't got those in! Cheers, Jon.
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