It is not only about pressure. In a tube, the getter is used to remove the last few gas molecules. At altitude, although the pressure is OK, there will be a continous supply of gas molecules, causing rapid cathode detoriation.
-- RoRo
Use zen...BE the drip.......
Ever hear of a ceramic cathode ? A local CRT rebuilder around here used rep lacvment guns with ceramic cathodes. The picture was a little different bec ause it did affect the gain of the tube somehow, but it looked better than it did before, and they lasted forever.
I wonder if scope tubes use them because it has been a long tie since I've seen one with a weak CRT. I got a Tek 561A that'll burn your eyeballs out i f you turn it too high. That was built before I was was born.
Anyway, how high do you have to get ? High enough to get online and get a p air of (I think) 6550s for like $75 if you're lucky and put in your credit card number. Or high enough just to listen to mono, which takes an extra jo int.
First you take your glove off and expose your hand to the vacuum, and then - oh wait, we can stop there, your hand has just been freeze-dried.
-- Tim Wescott Control systems, embedded software and circuit design I'm looking for work! See my website if you're interested http://www.wescottdesign.com
The 6L6 is a steel cased tube. How would you break it?
-- Never piss off an Engineer! They don't get mad. They don't get even. They go for over unity! ;-)
He probably means the 6L6GB - a later (cheaper?) variant with a glass envelope.
The 6L6-G looks best.
-- Tim Wescott Control systems, embedded software and circuit design I'm looking for work! See my website if you're interested http://www.wescottdesign.com
** Of course he did, metal 6L6 tubes are not used in guitar amps.
The type recently passed the 70 year milestone of continuous production with no end in sight.
.... Phil
** Of course that should be 80 year milestone.
The Wiki needs updating.
.... Phil
Don't your's flash purple if you whack the strings hard enough? No need for CRT-type vacuum. Might only be 1e-3 Torr.
And wasn't there a '50s James Blish short story with vacuum-based animals o n a large asteroid, with "smell imaging?" The mean free path was tens of meters, and they'd evolved the ability to see via molecular beams from heat ed ground (or from hot prey animals.) The bad guys' outgassing warm space suits were attracting the vacuum-based predators to attack.
Common misconception -- that's electrons escaping through holes in the plate, bombarding the glass, which fluoresces from high UV / soft x-rays / electrons.
I've also seen blue glow from innocent little tubes like 12AU7s and 6SN7s, but only at higher voltages. It's a combination of excess energy (enough to escape the plate and still excite the glass) and intensity (enough to be visible).
I've also seen a few types of plate material, where the fluorescence is visible on the inside coating of the plate. But definitely not a volumetric (ionized gas) thing!
Gassy tubes have a distinctive volumetric glow, in the electron beam area. You can also recognize atomic lines of popular gasses (most often Ar and N2), if you have a keen eye (and a diffraction grating!). The others are more diffuse: wide fluorescence peaks, or continuum radiation.
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
-- Nice. John Fields.
A few tokes should do it.
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