Unbearably Loud Static Noise from one failing 6080WB tube?

[dludingt]

Good evening all,

I have a V1 Crack with Speedball I've been enjoying for over a decade. I've made a lot of the typical upgrades with no issues. The other week I was fortunate enough to found a small stash of Tung-Sol branded 6080WB tubes with the solid graphite plates. All of them tested almost new on my tube tester with no shorts or emissions. They're beefy tubes and sound great!

Except one.

One of these tubes worked well for about 10 minutes then started producing an unbearably loud static/white noise. Loud enough I could hear it from halfway across my house.  I powered down the amp and all of the other 6080, 6AS7G, or 7236 I have on hand all work fine. Is the tube failing or could the pins be dirty enough to cause something to go haywire after warming up?

Thanks in advance for the help.

[Paul Birkeland]

I bet if you look deeply inside the tube while it's running that you'll see little arcs and sparks flying around in there.  I've seen this happen from tubes that are gassy, and now and then from 6080s where the white cathode material is flaking off for some reason.  I'd recommend just tossing that tube and not using it. 

[dludingt]

@

I bet if you look deeply inside the tube while it's running that you'll see little arcs and sparks flying around in there.  I've seen this happen from tubes that are gassy, and now and then from 6080s where the white cathode material is flaking off for some reason.  I'd recommend just tossing that tube and not using it. 

I just tried the potentially faulty tube and the flashing is fully intact and there doesn't appear to be any arcing or sparking inside when it makes the screeching noise after a long warm up. I guess I won't use the tube but I'm curious why this one single tube makes the awful sound and none of the others do. It's definitely an issue with the 6080 since it is very loud no matter what the volume pot is set to.

Thanks again for the reply!

[Tom-s]

The way to check is to put this tube under test on a full load tester.
So that's usually a parametric tester that runs a tube at its full potential (near or at maximum dissipation).
This way it fully warms up. Once warm repeat the short tests on this tester and the issue will show itself.

On a emission tester it's not under full load in most cases; and/or without any anode/cathode current at all; when not pressing the "measurement" button.
As a result the tube never gets truly warm (as when in use) and some leakages just won't show.

As PB recommended don't use the tube. It could be a problem waiting to happen.