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I have seen pictures over the last few years of 6550B and EL34 Svetlanas that have no silver flashing whatsoever; the ads claim "clear gettering materials." I must admit ignorance of these clear gettering materials. What is the story? The cynic in me suggests that materials shortages of getter chemicals was not enough to stop the production line.. but those tubes would have a short(er) lifespan to say the least. Victor K? Par? Robert H? Anyone? Thanks, Chris
Follow Ups:
Yes, it's a pill getter, taken from transmitter tube construction, and the getter stays more active over the entire lifespan of the tube. It's similar to how 211's, 845's, and the svetlana 811's are made. Tony
Since I qualify as "anybody"...Can't speak about the EL34s but regarding 6550s, you're no doubt referring to the Svetlana 6550B-3. These were the second incarnation of the SV 6550 from what I can tell (6550C is latest and current). They employ what I've heard referred to as a "pill" getter. They look like sintered metal discs attached to the plates where the flanges are welded together: one on each side of the plate strucure. There is no silver getter flash as received. After a few hundred hours of use, mine began to show a silvery like flash at the dome of the bulb like a normal getter. Not sure if this is intended or just a harmless artifact of operation.Apparently pill getters are just a different way of doing the gettering thing. May not require the induction heater during the evacuating process either. Since they're attached to the plates and seem to be heat activated, it would appear that this method would provide gettering action when most needed: the hotter the plates, the more gettering action although I'm not sure of that.
I was told when purchasing these things that the B3 version was created because the original B required a long burn in before the tubes would hold a stable bias. I can vouch for the burn in requirement for the B version. However, the B3s I bought were no better in that regard so maybe it was a production process/materials sourcing issue that brought us the B3. Regardless, once burned in (~24hrs) my B3s have got hundreds of stable hours on them in my MK3s (modified for individual bias adj).
Hi Steve O.,I had a quad of these Svetlana 6550B-3 tubes and gave me a few years of good service. These were tough indeed. A beautiful tube with the clear glass envelope. After a couple of days burn in they settled nicely.
CM
Thanks, Steve. I admire your knowledge and willingness to share you info. In your opinion, with regular "flashed" getters, could the heat from the tube cause what I often see as "getter rejuvination?" This is especially prominent in very used Mullard EL34s with small, brown getters that were run at low B+ and anode current. I run EL34s at the brink of meltdown, 500VDC, 60-65 ma plates+screens current,and the heat generated seems to replenish the getter flashing. Sometimes a round, dark ring will appear that may be coming from the "O" halo getter. In "DD" getter tubes, a dark ring appears that crosses over itself. This isn't vaporized screen metal deposits... your thought will be appeciated. I apologize for my rudeness in the past-- I'm flaky and having money, family and etc difficulties, but in 2-3 weeks I begin my first Electrician install, doing the complete install from the blueprints on up. My mood should improve when my cash flow does :0) Chris
My experience with rejuvinating the conventional flash getter is not positive. I've tried running them really hot in a test set-up for a day or so and the getter just doesn't come back. When the getter goes in the tubes I use, they seem to act gassy and I just toss em or use em for diaplay. I've never been able to bring back one with low emission/gm either but I've heard others have done this so I guess it's possible.Apology not really necessary here since there were lessons and I was a student...but thanks anyway.
Good luck in your new career.
...I know what you mean . The getter disc is disc-like but with depth , I think the gettering is countained within this object . The Svetlana 6C19 and EL36 also share this . I think zirconium is the compound used...FB
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