I bought a NOS 84/6Z4 that shows a short but tests good. I put it in my Eico 625 with the power off and set all the switches, then I turn the power on and get a strong short light but when I hit the test button it tests good. What gives?

:I bought a NOS 84/6Z4 that shows a short but tests good. I put it in my Eico 625 with the power off and set all the switches, then I turn the power on and get a strong short light but when I hit the test button it tests good. What gives?
:

That tube should not show a short on any setting. 1 and 5 are the filament, 4 is the cathode and 2 and 3 are the plates. If you have a heater-cathode short it should not be used; it would be like the directly heated cathode rectifiers (5Y3 etc) in which the B+ is present on the filament supply line.
Johnnysan-

Any NOS tube can be bad. Never know how many times it has been handled dropped, and bouced around. If you look closely, it may even show bent elements.

What I'm wondering is,if the shorts light was on,why did you go ahead and test it?The shorts light is supposed to keep you from testing a shorted tube and damaging your tube tester.

Just thick I guess

Just thick I guess