[sdiy] calling tube gurus...this old rare one has the most peculiar filament problem

[Bob Weigel]

What could be going on here.   I've got a Teisco amp ..a very old one 
that I'm repairing for a guy who does the Teisco amp page.  It uses a 
6Z-DH3A  and yup that is the actual tube number. It's a preamp tube.  I 
fortunately have a working one but it measure real low on quality 
check.  But at least it lights up.  This one does not HOWEVER...both 
filements measure good on dc test. Both a little under 4ohms.  3.5 and 
3.8 on the bad one..which..is actually a brand new tube I believe.

Resoldered the bottom but did no good but now I see that it obviously 
wouldn't.  That filament is stone cold but theo ther lights in my 
Jackson tester.  I get no measure on it of course at all since the 
filament..really really isn't lighting at all.  I can shield the tube 
from light and there is no glow at all. -Bob