Yeah
Gosh, I sure am glad algore had only invented this interwebz thingy in the 80s so you didn't get the chance to voice your opinion on the subject some 75 years ago when field emission microscope was invented - who knows, the guys working on it might have just dropped everything and focused on something more promising instead (nuclear bomb for the other side ?
).The devices that can leak current in the opposite direction when reverse biased even though according to you this couldn't possibly be happening ? Why yes, I do
Attachments
I'm sceptical about this. The anode-to-glass interface could be described as having themal inertia (even though it is primarily by radiation). If you cool the ambient temp and glass with forced air, surely you will increase the net thermal inertia and so you will cool the anode too, at least a little bit?
And internal RF shielding.
Hmm, I forget offhand if the 807 is rated for more power dissipation. Seems to me it has more space inside than a 6L6G = lower glass temperature for a given plate dissipation.
Tim
one ends with a G and the other one ends with a question mark.........I think
oh yes........... the heater heats the K then the electrons leave which does not make them go to the anode plate [much]
what does that is more like magnetism ( electron draw )
ELECTRON DRAW the negative wire is a supply of negative and electrons are negative........................so the negative wire supplies electrons
and with that the anode plate connected to the positive wire is an electron draw....kind of ?
oh yes........... the heater heats the K then the electrons leave which does not make them go to the anode plate [much]
what does that is more like magnetism ( electron draw )
ELECTRON DRAW the negative wire is a supply of negative and electrons are negative........................so the negative wire supplies electrons
and with that the anode plate connected to the positive wire is an electron draw....kind of ?
Sure you can cool the plate a little bit by cooling the glass(most likely a VERY little bit, probably so little that it doesn't matter), but you won't make the cathode cold like some were worried might happen.
Where did I say that?
It's called a thermionic diode. Look it up on wikipedia like I did and see what an utter public fool you have made of yourself.
'electrons are not easily released from the unheated anode surface when the voltage polarity is reversed. Hence, any reverse flow is negligible'
w
It works because the cathode is HOT and the anode is NOT. What on earth do you imagine the heater is in there for?
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Gosh, I sure am glad algore had only invented this interwebz thingy in the 80s so you didn't get the chance to voice your opinion on the subject some 75 years ago when field emission microscope was invented - who knows, the guys working on it might have just dropped everything and focused on something more promising instead (nuclear bomb for the other side ? ).
/QUOTE]
I think Muller would have stayed focused on his FEM.
)./QUOTE]
I think Muller would have stayed focused on his FEM.
Strange argument
Ok, I should stay out of this, but what a bizarre argument.
The valves we use are electrostatic devices. Heating the cathode allows a larger than unheated electron cloud, that then can move to the plate, assisted or opposed by electrical potential gradients. This may occur with or without heated cathode, but heating allows us to use usable voltages (potentials), otherwise all these tubes would require massively high and dangerous voltages to move electrons in convenient ways.
Heat alone will create a cloud of electrons and stray potentials will move some of them, but not necessarily in ways we desire.
From the wikipedia entry for "thermionic diode":
"The principle was independently rediscovered by Thomas Edison on February 13, 1880. At the time Edison was carrying out research into why the filaments of his carbon-filament light bulbs nearly always burned out at the positive-connected end. He had a special bulb made with a metal plate sealed into the glass envelope, and he was able to confirm that an invisible current could be drawn from the glowing filament through the vacuum to the metal plate, but only when the plate was connected to the positive supply."
Note the last sentence. An electrical potential is required, otherwise no significant, or useful, current will flow. that is simply physics and electronics.
I think everyone arguing here understands how this works, including Wakibaki, but he is emphasising one part.
"A tube works precisely because of the temperature difference between the cathode and the anode. Work function be damned, this is the only difference between the cathode and the anode in a primitive tube diode, and is the reason why current only flows in one direction."
This is not the only difference, the other is a potential between the cathode and the anode, even in Tom Edisons first tube. Always has been and always will be the case, I am afraid.
Ok, I should stay out of this, but what a bizarre argument.
The valves we use are electrostatic devices. Heating the cathode allows a larger than unheated electron cloud, that then can move to the plate, assisted or opposed by electrical potential gradients. This may occur with or without heated cathode, but heating allows us to use usable voltages (potentials), otherwise all these tubes would require massively high and dangerous voltages to move electrons in convenient ways.
Heat alone will create a cloud of electrons and stray potentials will move some of them, but not necessarily in ways we desire.
From the wikipedia entry for "thermionic diode":
"The principle was independently rediscovered by Thomas Edison on February 13, 1880. At the time Edison was carrying out research into why the filaments of his carbon-filament light bulbs nearly always burned out at the positive-connected end. He had a special bulb made with a metal plate sealed into the glass envelope, and he was able to confirm that an invisible current could be drawn from the glowing filament through the vacuum to the metal plate, but only when the plate was connected to the positive supply."
Note the last sentence. An electrical potential is required, otherwise no significant, or useful, current will flow. that is simply physics and electronics.
I think everyone arguing here understands how this works, including Wakibaki, but he is emphasising one part.
"A tube works precisely because of the temperature difference between the cathode and the anode. Work function be damned, this is the only difference between the cathode and the anode in a primitive tube diode, and is the reason why current only flows in one direction."
This is not the only difference, the other is a potential between the cathode and the anode, even in Tom Edisons first tube. Always has been and always will be the case, I am afraid.
Do you mean difference of max power dissipation by 6L6G and 807 does not matter?
Also, somebody wrote already here (Tubelab?) about crude experiments with oil cooling of 6L6 envelope.
Black anodized bronze bracelets were used in military transmitters as heatsinks around glass tubes.
Yes, I hesitated to join in when the tone of conversation resembles one of the other audio forums, so I will just state a few facts.
1) I have pushed a few tubes hard enough to cause rapid failure. I usually dissasemble the tube to find the cause. The only time I have seen cathode damage is when there was an arc. The arc is usually caused by gas. The gas can be from an air leak, or outgassed impurities released from glowing electrodes. My belief (OK not a fact) is that if you got the plate hot enough to overheat the cathode, you are about to melt the glass.
2) I have a friend who succesfully runs 2C39's at about 200 watts of dissipation (twice the rating) each by direct water cooling. These are external anode tubes so the cooling water is flowing through an aluminium block in direct contact with the plate. The application is an RF power amplifier at 1296 MHz. It works just fine and still runs the original tubes after almost 3 years of use. Plate voltage is 1800 volts, again way over spec.
3) There were stories of ham radio operators extracting big power from the old metal 6L6's by immersing them in oil in the post WWII era. We had hundreds of brand new RCA metal 6L6's back in the technical high school that I attended (military surplus). I performed numerous experiment on these tubes over a 3 year vocational electronics program. I got plenty of power out of them without benefits of additional cooling but the paint peeled off of them rather quickly. Operating the tubes inverted in a fish tank full of water did not improve the power output or distortion, but did preserve the paint. Tube lifetime was rather random, measured in days or even hours, and did not seem affected by water cooling.
4) I have proven that the screen grid will emit plenty of electrons which will travel to the more positively charged plate if you get it glowing hot enough. Screen drive experiments taken a bit too far.
5) Yes, a glowing plate can and will emit enough electrons to conduct plenty of current to another plate in the same tube (amps!). Purposeful experiments of some 6AS7's with one dead section.
Like I said, probably glass operating temperature. The plate is the same size, so it will have about the same thermal resistivity, but the glass will have lower resistivity, therefore allowing more power. But doesn't this allow the plate to get hotter? Yes, it will. Evidently, not hot enough to go over limits.
Cooling the glass from ~200C down to 25C will cause the same temperature change inside, so the plate might go from 500C (not quite glowing) to about 400C. It's still about as hot, so it doesn't really matter.
It's worth noting that radiative loss is highly nonlinear, i.e. it goes as t^4. So thermal resistance (a linear term) isn't very useful, because you're pretty far up the exponent and the slope is much steeper than deltaT/Pdiss. That also means that temperature is more of an absolute function of power, rather than power going as the difference of temperatures (as it does in solid matter). Whereas the glass might change 200C, the plate might change 50C or less. Which is also convienient when you're overheating the plate, and screen, and grid, and the cathode sees all of this, and doesn't really care because it's a good bit hotter (once you get into red plate territory, you're going to have an effect, though, resulting in cathode overheating, for which you should reduce heater power to maintain lifetime -- not that you'll have much lifetime from the other electrodes at that power level anyway!).
Tim
Don't forget on alot of power tubes the getter is vapourised inside the envelope on top of tube and relies over 100°C to function properly. I'm against overcooling, more important is to keep chassis ventilation clear and components underneath properly ventilated. If one adds a fan to a power amp and hears it whilst on quiet music passages, that's as good as a useless s/N ratio and distortion.
richy
richy
Sometimes I think Diyaudio needs an official troll handling protocol, especially for the ones who think blatant trolling is educational if it forces people to research and better understand the topic. I find that a weak defense for a behavior that can litter our archives with bogus ideas stated as facts just waiting for an unsuspecting future searcher who gets the troll's "answer" without the context to know it's intentionally incorrect.
Most tubes use a heater to free electrons from the cathode. That is a fact. In that sense it could be said that your average tube only "works" if the cathode is hot. That doesn't prove that temperature gradient is responsible for controlling the flow of electrons from cathode to anode though. You've given the perfect example, a vacuum tube diode. Current flows through the tube when the anode is more positive than the cathode, but when the anode voltage is lower than the cathode the flow is stopped. In your world we would have to heat and cool the anode above and below the cathode to achieve this basic rectifying effect. Do you see any heater and cooler pins on the anode?
[Offending paragraph removed by moderator]
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I remember the experiment in school with the cathode ray tube, just like yesterday.
The device itself resembled a conical laboratory flask of perhaps a litre with the flat bottom covered with a thin white coating. The device was set up in a standard lab clamp with the white 'screen' vertical and visible. Inside the tube close to the screen a metal foil in the shape of a Maltese cross was attached to a sturdy wire support which was fused through the conical wall. This was the anode. At the neck, a further metal assembly comprised the cathode and heater.
The tube was connected to the vacuum pump and the air in the tube was exhausted. A low voltage was applied to the heater and connections from the cathode and anode were run to the Van de Graaff generator, which ran off an electric motor.
The blinds were pulled.
As the evacuation proceeded the glow of ionised gas disappeared and eventually the effect of the 'cathode rays' became visible due to overshoot past the anode target leaving the Maltese cross silhouetted in black on green on the phosphor screen. They could then be perturbed with a magnet or a electrostatic field with visible effect. The HT connections were reversed to demonstrate the thermionic diode effect, and the heater current varied.
I said nothing controversial. Why do you think tubes have the structures they do? Electron flow is not the only consideration. A tube works because of the temperature difference between anode and cathode. Anode and cathode are connected by the tube structure. In operation, a temperature gradient exists between anode and cathode, necessary to the functioning of the valve. If the gradient is not maintained, the valve ceases to function. This may not be the way in which you are accustomed to looking at things, but the context is heat flow. Get used to it. I may be introducing other unfamiliar ways of looking at things...
w
It was only 45 years ago. Something about grannys and eggs....
The device itself resembled a conical laboratory flask of perhaps a litre with the flat bottom covered with a thin white coating. The device was set up in a standard lab clamp with the white 'screen' vertical and visible. Inside the tube close to the screen a metal foil in the shape of a Maltese cross was attached to a sturdy wire support which was fused through the conical wall. This was the anode. At the neck, a further metal assembly comprised the cathode and heater.
The tube was connected to the vacuum pump and the air in the tube was exhausted. A low voltage was applied to the heater and connections from the cathode and anode were run to the Van de Graaff generator, which ran off an electric motor.
The blinds were pulled.
As the evacuation proceeded the glow of ionised gas disappeared and eventually the effect of the 'cathode rays' became visible due to overshoot past the anode target leaving the Maltese cross silhouetted in black on green on the phosphor screen. They could then be perturbed with a magnet or a electrostatic field with visible effect. The HT connections were reversed to demonstrate the thermionic diode effect, and the heater current varied.
I said nothing controversial. Why do you think tubes have the structures they do? Electron flow is not the only consideration. A tube works because of the temperature difference between anode and cathode. Anode and cathode are connected by the tube structure. In operation, a temperature gradient exists between anode and cathode, necessary to the functioning of the valve. If the gradient is not maintained, the valve ceases to function. This may not be the way in which you are accustomed to looking at things, but the context is heat flow. Get used to it. I may be introducing other unfamiliar ways of looking at things...
w
It was only 45 years ago. Something about grannys and eggs....
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