tube white noise.

O.k. so I know that I had a bad tube and I replaced it. No more noise in the audio. But I am wondering how white noise low in volume would be on a tube?

> I am wondering how white noise low in volume would be on a tube?

I am wondering what you are asking. I think your keyboard mangled the sentence.

"how low"?  A couple micro volts.

"how white"? There's always a 1/f red-pink component, but inaudible in many audio systems.

Why is there noise? There is noise EVERYWHERE. You can even calculate an estimated value. My "A couple micro volts" is based on tube Gm about 1/1K, tube temperature about three times higher than room temp, and "hiss" implying audio bandwidth. You do something with the charge on the electron and those factors, you get a "minimum noise". 1%-10% of tubes will have just-audible to gross-loud Excess Noise, dirt on the cathode etc.

your right that was very mangled. Sorry for that Prr.  So I have a tube with a dirty cathode, looks like I better take the glass off and clean it. Just kidding... I put the tube in the trash.

> I better take the glass off and clean it.

Use fine Brillo on a toothpick, then flush with boiling nitric acid.

> Just kidding... I put the tube in the trash.

That's like the Three Stooges, throwing away half the nails because the heads are on the wrong end. Dummy, those go on the other side of the house!

Seriously: tubes with a mild hiss are fine in higher level stages, preamp outputs or power-amp driver stages. Hiss is mostly an issue right AT a passive pickup (mike, gitar, phono) or volume control wiper. That stage has gain of 10-50, so the next stage can often have huge excess noise and it won't be noticed.

Why was the blond fired from quality control at the m&m factory?


-she kept throwing away all the ones with a W on them...


I know, I know, I'm sorry...