Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dscottguitars on February 26, 2013, 01:50:51 pm
-
I this tube bad? It is a Sylvania 6L6GC, top round getter. The getter has no metal in it like the other matching tube I have. On my meter the needle goes all the way up instantly. The short light blinks a bit when warming up but once warm it stops.
The last pic shows the tube with the metal in the round getter. The meter reads about 49 on this one.
Thanks,
Daniel
-
If it pegs the meter when a known good tube doesn't, it is probably shorted or gassy.
Don't know what you mean by "getter has no metal in it" as I see the silvery getter on the top of the tube. It does, however, appear smaller than typical which might be an indication that the getter was once bigger but has been partially depleted by recombining with gas in the tube. Or, it might mean the getter flash was always smaller than typical.
I don't know if you should test the tube in an amp; if you did, you'd want to clip a meter in place to measure cathode current, switch the power on and be prepared to switch it off immediately if current climbs without settling or if the tube redplates/flashes. a massive failure should still only pop a properly-rated fuse, and you'd see right away if the tube was acting up.
-
one of the getters is filled in with a metallic substance, you can see that in the 3rd picture, you can't see the green towel through it, but you can on the first one.
-
That just means the getter flash has been doing its job of recombining with stray gas molecules in the tube.
-
Where the silver of the getter has faded to a sort of smoky brown residue on the glass adjacent to the remaining silver area, its a sign of a worn out tube (like the one on the r.h.s. of this pic)
(http://www.turneraudio.com.au/monobloc-se32-13e1-cfb-2012version_files/13E1-worn-getter2-may2-2012.jpg)
from this page
http://www.turneraudio.com.au/monobloc-se32-13e1-cfb-2012version.html (http://www.turneraudio.com.au/monobloc-se32-13e1-cfb-2012version.html)
-
Just keep in mind that some getters (notably for old western European types) were silvery-black from the day they were made. Seeing that rather than pure silver does not indicate a worn or abused tube.
You'll most often come across those with old European Philips (not later Philips ECG), Mullard (which was part of the Philips empire), Amperex (ditto, a Philips company) and occasionally Siemens or Telefunken tubes.
-
I have that same tester! I don't put a lot of stock in its findings but it did identify a 5V4 that really was weak.
It also has an intermittent "short" light that lights up on tubes I know are good.