Eimac and their predecessors Heinz and Kaufmann (Gammatron) don't getter like receiving valves. There's no barium getter flash on the envelope; they only stay gettered by their hot anodes. They must run at red hot anodes. Great, great stuff, but must not be treated like a receiving valve. 2A3's, 300B's and such have oxide filaments (cathodes). 211's, 845's and such have thoriated tungsten filaments (cathodes) with white hot filaments, but all of these have barium flash getters and want below-red anodes. The H&K / Eimac family requires red-hot anodes for gettering, and has anode (and often G1) protrusions through the glass envelope, so aren't popular - an opportunity for diyAudio folk.
To use the H&K/EiMac valves in a modern translation requires that we re-getter the old (possibly Big War era) valves and see who still has less than (pick a number) of microamps of grid current after a re-gettering process and KiloJolt slug. A pair of H&K/EiMac or RCA or whatever 4E27/Gammatron 257B/5-125 valves goes for nothing compared to a pair of real RCA 845's, but run well at 600VDC instead of 1000VDC, and with 5VAC (also thoriated tungsten) filament, Mu (triode connected) is about 5, like a 2A3, a 300B, an 845, etc. Curves are even better. What's nor to like?
All good wishes,
Chris
To use the H&K/EiMac valves in a modern translation requires that we re-getter the old (possibly Big War era) valves and see who still has less than (pick a number) of microamps of grid current after a re-gettering process and KiloJolt slug. A pair of H&K/EiMac or RCA or whatever 4E27/Gammatron 257B/5-125 valves goes for nothing compared to a pair of real RCA 845's, but run well at 600VDC instead of 1000VDC, and with 5VAC (also thoriated tungsten) filament, Mu (triode connected) is about 5, like a 2A3, a 300B, an 845, etc. Curves are even better. What's nor to like?
All good wishes,
Chris
There will be an equlibrium between the produced heat and the outward radiated and conducted (via pins etc) heat. So the temp will stabilize. Otherwise the temp would rise to over 1M degrees (conservatively ;-).
Jan
It doesn't really matter: only the 4th power law matters (neglecting losses from the connections, supports, etc).
It is counterintuitive because it means that the thermal resistivity in the vacuum (where only radiative exchanges are possible) depends on the absolute temperature: at very high temperatures, the thermal resistance becomes vanishingly low
There does have to be some practical simplifications made in order to relate the fundamental physics relationships of thermal radiation in a vacuum from one black body to another black body, to an example situation like an output stage valve. The RCA book goes in to how some practical aspects of a tube are handled when starting from basic physics analysis. The plate temperature is certainly a function of electron flow, which is simplified to a power dissipation in the plate metal, and that is melded with radiative transfer from the cathode region, and to the glass/external. Many nuances exist, like the heat conduction in and through the plate structure (as easily seen in photos of red-plating anodes where the region of red-plating is highly influenced by electron flow) and how the plate structure can vary between valve makes - such as from wings to increase radiative area, and plate material to increase heat conduction like including copper.
Manufacturers had to juggle many influences when deciding on plate structure and metal, and glass shape and surface area, as managing outgassing and service life was a major issue.
Manufacturers had to juggle many influences when deciding on plate structure and metal, and glass shape and surface area, as managing outgassing and service life was a major issue.
Of course it is. Vacuum or not has nothing to do with electron flow. Compare to the universe ;-).
BTW, the original question is easily answered. Just power up the heater and leave the anode voltage off. Does the tube get hot? Not really, it gets warm to the touch, but it only gets really hot when the anode voltage is switched on and power is dissipated.
QED.
Jan
The inside of the anode radiates to the 1. cathode 2. to itself (3. to the beam confining plates if it is a beam tetrode.)
The relation between 1 and 2 depends on 1. geometry 2. the surface area ratio 3. the 4th power of cathode temperature 4. the 4th power of anode temperature 5. the emissivity of cathode and anode.
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In the end, the anode encloses completely all of the rest (neglecting losses, etc). This means that all of the energy generated inside has to be dissipated by the anode, and the cathode needs to find its final equilibrium temperature based on its own dissipation, and the temperature of its surroundings (the anode in this case)
Imho, people get too confused when radiation transfer talks about "the anode radiates to the cathode". Far simpler and more insightful to just say the cathode radiates heat to the anode inner surface because the anode is colder, and similarly the anode outer surface radiates heat to the glass because the glass is colder.
With respect to heat flow in Watt, the cathode radiates away the heater power level, and the anode radiates away the heater power level and the anode dissipation level (and screen power). The glass has to transfer all that power externally through a combination of mainly convection, with some radiation.
With respect to heat flow in Watt, the cathode radiates away the heater power level, and the anode radiates away the heater power level and the anode dissipation level (and screen power). The glass has to transfer all that power externally through a combination of mainly convection, with some radiation.
We have G2 , G1 and maybe more electrodes inside , Much more important to be cool . Besides normal heating from current I can't find anything related to radiation from plate ... if that would have been significant and concerning many books on the subject would be available
And again , if electrons flow inside the vacuum model is completly false .
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How so? What is vacuum?
If a radio works in space, does tthat mean there is no vacuum in space?
Jan
From a technological, operational, POV maybe but from a thermodynamic POV, it doesn't matter in the least, even if they melt down: all their heat will be transferred to the anode, and eventually the glass envelope
Electrons do play a role: they have the ability to transfer heat, but the devil is in the details, and determining the exact amount of heat taken way under given conditions requires an expert understanding, and being no expert, I am not going to venture into this fieldBesides normal heating from current I can't find anything related to radiation from plate ... if that would have been significant and concerning many books on the subject would be available
And again , if electrons flow inside the vacuum model is completly false .
Vacuum is the absence of matter , below a certain density .
When the tube is conducting and the space inside is filled with electrons it is not a vacuum , for the radiation of heat could be everything .
For the purposes of electrons travelling between cathode and anode, the space is a vacuum whereby any molecules have been evacuated at manufacture and the getter continues that evacuation as molecules outgas over time - it is a hard vacuum (there are various grades of vacuum). There is a local electron cloud around the cathode, and electrons stream from that cloud to the anode, but electrons are miniscule relative to molecules. Heat radiation by photons effectively do not interact with the electrons - its hard enough getting anything to interact with photons, even in the LHC.
You have a complete false picture. The elctron cloud is is infinitisimal small and certainly does not change the vacuum.. if that would have been significant and concerning many books on the subject would be available
And again , if electrons flow inside the vacuum model is completly false .
And those books are available, lots of it, but not in audio. A hot material ALWAYS radiates to a less hot ambient, it's a basic thing in physics.
Those books describe how that radiation happens depending on the temperature differences in the system, the material of the radiating body, the color of the radiating (and absorbing) body, and such. You should look it up.
Jan
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OMG , you don't know that the current is made of electrons ? Calculate how many flow at 100mA plate current . We are talking about plate beeing hot from electron bombardment ... in this case vacuum is for sure changed .
And about the heat transfer what you say is nonsense , maybe you should read those books . Of course the coolest will radiate also to the hottest until the equilibrium is reached . By the way , for radiation the temperature difference is unimportant ... That's why I said that maybe because of the electron flow the radiation from anode can't heat up the inside of the tube .