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YT2095UK · 6th Sep 2009, 10:24 am

I was just going through one of my boxes of valves to try and sort/organise them a little better and came across 4 PL81`s, but they all seem to have some sort of Black/Brown deposit inside them, something akin to creosote to look at.
the getters all seem fine and since they are from different makers I can practically rule out some sort of contamination during manufacture.
one of them is in a Really sorry looking state with the 2 fins at the top that are spot welded to the copper posts at what Looks like G1 having a crackle effect like the plating is flaking off almost peeling off in places.
now I`v seen times where there has been a hole in a plate and you get a rainbow effect on the glass probably from some sort of vaporised metal carried as Ions and then reformed on the glass as it loses an electron, but this black stuff is nothing like that.

anyone Know what it is? and is it indicative of a dud valve?

6th Sep 2009, 10:24 am	#1
YT2095UK Retired Dormant Member Join Date: Sep 2009 Posts: 487	"Black" PL81s I was just going through one of my boxes of valves to try and sort/organise them a little better and came across 4 PL81`s, but they all seem to have some sort of Black/Brown deposit inside them, something akin to creosote to look at. the getters all seem fine and since they are from different makers I can practically rule out some sort of contamination during manufacture. one of them is in a Really sorry looking state with the 2 fins at the top that are spot welded to the copper posts at what Looks like G1 having a crackle effect like the plating is flaking off almost peeling off in places. now I`v seen times where there has been a hole in a plate and you get a rainbow effect on the glass probably from some sort of vaporised metal carried as Ions and then reformed on the glass as it loses an electron, but this black stuff is nothing like that. anyone Know what it is? and is it indicative of a dud valve?