Tube flash

Pre amp or power tube flash?

Try lightly tapping the tube with a pencil eraser while it is on the tester, to make sure the tube doesn't have a marginal short circuit.

Also, it's possible that something else failed in the amp that caused the tube to flash. For instance if a coupling capacitor connected to the grid broke down, it might have put a large positive voltage on the grid, causing the tube to flash.

Regards,
-- Al

I think I see where Stevecham is going with his question - Amperex (Holland) small signal tubes will 'flash' when first powered up, and it's totally normal with those tubes.

On the other hand, I've had power output tubes 'flash' on me, blow a fuse, and test fine afterwards (all EL34's for what it's worth) but I've learned to think of my tube tester as a rough way to weed out obviously failed tubes, not a final arbiter of good tube vs. bad tube. A lot of my tubes have tested well, but were noisy/fuzzy or microphonic or had less output than a tube used in the opposite channel that tested exactly the same.

Have you seen those old Upscale Audio ads that say "we don't use your amp as a tube tester!"? Don't use yours as one! If an output tube flashed, don't risk putting it back in your amp, regardless of what your tester is telling you.

Just my opinion, of course. Good luck!

Do tubes come already gettered?
Would the flash be the last oxygen in the tube being consumed?

If this happened on a tube in-service, I'd remove it from the circuit.

don't use your amp as a tube tester?! how COULD you?

don't use your amp as a tube tester?! how COULD you?
04-02-10: Magfan

Well lets see... the tubed flashed in the equipment. The tube was pulled and tested ok in the tester.
Put the tube back in the equipment, maybe flashes again but this time damages an electrical component or trace on a circuit board.
Yep maybe the tube was bad after all..... Hell of a way to find out, use the amp for a definitive test.

Is it possible for a tube to flash, blow the fuse in the amp, and then test ok on a tube tester? Or is my tube tester broken?
Jaffeassc

May not be the tube that caused the fuse to blow.... Might be though....