Detached getter?

[rknize]

I've never seen anything quite like this. It's an eBay tube. The description was sketchy but they were supposedly tested. Looking carefully at the original eBay ad, I can see the missing getter in the pic. There are bits of getter floating around in there, so I suspect this tube is not safe to use.

It almost looks like some kind of arcing happened, because the getter is blown onto the glass base where the support wires all come together. Strange.

Russ

 

[Geek]

How hot he get that thing 😱

 

[ktuuri]

I have had the rectangular part of the getter fall off its support rod and land in the bottom, everything works fine, but yours looks like it exploded.

 

[HollowState]

I cannot help thinking that at some time someone tried to reflash the getter under an RF induction heater to improve and restore the film coating inside the glass. Bringing the tube's getter into close proximity to the work coil of a relatively small bench top heater (sometimes called a bombarder) is the method used. But often this fails to produce good results because once originally heated and cooled, the getter's chemistry is depleted. Too much power and/or time spent heating produces the results you see if the getter's closed loop didn't open first. Trying to restore used tubes was not that uncommon years ago by some surplus dealers.

I would imagine if you used the tube vertically and kept the loose pieces at the bottom of the envelope, it should work ok.

 

[Tubelab_com]

I have an old tube with some of the getter material floating loose inside it. It still works, and coincidentally it is a 45 that I got on Ebay. I bought 3 used 45 tubes for $12 because they were sold as "weak" and the loose getter material on one tube was mentioned in the text. Yes it was several years ago.

 

[rknize]

Thanks. Trying to reflash the getter makes some sense based on the shape of the missing area and the way the getter got blasted onto bottom of the tube structure. The other tube's getter looks funny too and with the reflashing idea it may make sense. I can't really capture a picture of it, but it looks as if there are two layers of getter with a more faded larger area and a more opaque area at the bottom. Definitely not your typical worn-getter look.

Speaking of weird getters. I have another eBay 45 with a getter that looks fine (very shiny with little fading at the edges) except it is riddled with pin holes. Not unlike what you would see with car paint sprayed on a poorly prepped surface (fisheyes). The tube tests strong. I suspect it happened at manufacturing.

I don't own a tube tester, but with the adjustable fixed bias of the Tubelab SE I can measure delta Ia and delta Vg to calculate transconductance to compare with the operating points. How would I check for gas? Look for white noise on a scope? My ear against the left-versus-right tweeter?

 

[rknize]

I tapped on the tube a bunch to try to coax the flakes to the bottom, but the tube just crackled loudly and started drawing a lot of current. The other tube I mentioned about with the weird double-getter also has a funky kink in one of the filament courses. They are from the same lot. Having a filament touch the grid would probably make the MOSFET mad, so I will probably trash this tube too. It biased OK, though.

Caveat emptor eBay ID "mook44".