6B4G noise

[elbinster]

I finished up my switchable 6B4G/2A3/300B GSG last august and since then have noticed a burst-noise (digital noise?) like sound increasing whenever I have the 6B4G selected as the output tube. At first it's nice and quiet and not much of a problem, but as I listen longer I hear it more and more and slowly to go insane. It sounds exactly like the noise that computers always pump out of their on-the-motherboard sound card. The 2A3 has nothing of the sort (though has a different filament supply), and the 300B are also silent (and share all but a paralleled 1.5R resistor).

What was strange is that I happened to swap the left and right 6B4G and the noise followed. Further tests confirm the noise follows the 6B4G. (at least I can stop tinkering with the wiring beneath ).

Anyone know of why this could happen? Is it a sign of the tube's imminent death? I could try to get another few 6B4G tubes, but with a 2A3 and 300B a switch throw away, it's not high on my priority list. Maybe I'll just mark it with a big scarlet 'N' to indicate it's propensity towards noise

[Shannon Parks]

This just sounds like a particularly noisy 6B4G. I'd mark it and try to find another to pair up with the non-noisy one.

Shannon

[EWBrown]

Take a look inside the tube when it is operating, (from the top) and check if there is a blue or green glow INSIDE the plate, that would indicate a gassy tube. That would indicate the tube is near its end of usefulness, or was bad fron the start - usually from an incolplete vacuum or a very slow leak in teh pin to glass seals in the base of the tube.

A blue (or other color) glow on the inside of the glass envelope is normal, with most power tubes.

I have some Sovtek 2A3s which look like "plasma globes" when they are operating, but they sound OK - their colorful light show is on the inside of the envelope, and fortunately not inside the plates.

/ed B

[elbinster]

Thanks for the info guys. My 2A3s and 6B4Gs both put on nice light shows on their envelopes (I still think it's Cerenkov radiation), but I no longer have the option of looking inside the plate as the troublesome tube has ceased operation. No longer gets warm. Bummer, but as I have 2A3s and 300Bs on the same unit, I haven't been concerned with finding a new set just yet.

[EWBrown]

Cerenkov radiation is a somewhat different matter (I remember seeing that phenomenon live and in person, at the small research nuke reactor at URI back in 1968, in my early attempts at understanding a quantum physics course). Pretty glowing blue water

If the offending tube no longer gets warm, either the filament has opened, or the vacuum has been compromised, so that no plate current flows.

Any glow inside the elements, with the exception of reflected filament light, indicates a gassy tube. THis would typically be blue, greenish or purplish, depending on the nature of gassiness inside the tube.

Several years ago, I was given a NOS pair of brass-based WE 276As, and unfortunately, they proved out to be about as gassy as a bunch of big fat guys after a chili-eating and beer-drinking contest . I'd normally call these tubes JPFROG (Just Plain F***ing Ran Outa Gas), but actually, it was the opposite situation.

The gas wouldn't "ignite" at normal tube testing voltages, I had to run them with a high voltage (up to 800VDC) supply and a variac to get them to flash over. I gave them to Gary Kaufman, last I heard he was planning to mahe them into fancy lamp bases. Too nice to "plink", too bad to use

/ed B

[Ty_Bower]

My "new" Sovtek single plate 6B4G have a blue glow that sticks to the inside of the glass. It's most noticeable near the top of the envelope.


My very old Svetlana 6S4S have a different kind of blue. It's very deep and rich in color, and appears to come right off the surface of the plates themselves. Weird.

[Geek]

Cerenkov radiation is a somewhat different matter (I remember seeing that phenomenon live and in person, at the small research nuke reactor at URI back in 1968, in my early attempts at understanding a quantum physics course). Pretty glowing blue water

And pretty colours when starships pop in and out of warp

Cheres!

[EWBrown]

Then, recently I have heard some very interesting (even if not readily confirmable) stories about what occurs with a very rapidly 200,000 RPM or greater) spinning mercury vapor vortex and a bit of thorium oxide, and some controllable / focusable magnetic fields..

The WWII era German nazi scientists called it "The Bell", and the folks from ancient India called them "Vimanas". Apparently the German design could only go up and down, and was not manuverable.



/ed B