Getter flashing is caused by electrically or inductively heating the getter ring. The getter material deposited on the glass will react with any stray gases in the tube, but at room temperature that reaction will be many times slower than it was during the flashing process.
Chemical reactions such as the getter absorbing stray gases are temperature dependent (google Arrhenius if you want to know more). Roughly, every 10degC decrease in temperature halves the reaction rate.
All tubes have some very small level of leakage, which can result in significant amounts of gas diffusing into the partial vacuum of the tube envelope over the course of many decades; a 1920s vintage balloon tube like a 26, for example, may have been stored in an often cold warehouse for almost 90 years! At low temperatures, the reaction rate of the barium getter with the gas will be slowed considerably, and may actually be slower than the rate of gas ingression into the tube, hence residual gas levels will increase.
So, a heat treatment prior to use may in fact be a reasonable prophylactic measure, provided you do not melt the tube base via overzealousness.
I like heat the cathode for least 20 minutes, after it + 20 minutes with the HV(without music), and the tube are ready to do some music.
Michael Boele 6C33 datasheet say the minimum heat time(90% emission) for this tube in military use is 120 seconds, where it is grant for 1000 hours only.
But tubes vendors will disagree, as they want sell more tubes to the custumer, as early as possible.
Just noting a few things...
Seems to me that this is a lot of work for something that ought to happen when you start up the heaters or even run the tubes initially (and not baking means the bakelite bases stay nice looking). Maybe I haven't got such expensive tubes to try this on or the ones that I do have just aren't worth the effort.
But inherently knowing that this is a very short lived component (I have been told that useful life can be measured in the thousands of hours), I am not sure that I would want to even bother as I get my inspiration from people like George at tubelab. If there was a way I would want to push a tube to maximize performance, I would go with George's awesome methodology on pushing a tube.
I also have a feeling that those Solid State Class A guys must be reading some of these posts and scratching their heads wondering what all the fuss is about.
Seems to me that this is a lot of work for something that ought to happen when you start up the heaters or even run the tubes initially (and not baking means the bakelite bases stay nice looking). Maybe I haven't got such expensive tubes to try this on or the ones that I do have just aren't worth the effort.
But inherently knowing that this is a very short lived component (I have been told that useful life can be measured in the thousands of hours), I am not sure that I would want to even bother as I get my inspiration from people like George at tubelab. If there was a way I would want to push a tube to maximize performance, I would go with George's awesome methodology on pushing a tube.
I also have a feeling that those Solid State Class A guys must be reading some of these posts and scratching their heads wondering what all the fuss is about.
Thought about it. Looked up designs for induction heaters but never bothered to try.
Popped a couple in a microwave.
Don't bother.
I afraid activate the getter and degassing a NOS tube is not this fast, it is a slow process to some hours or days if one had a 6V eletrical heater for the cathode.
Powering any cold tube with the high voltage B+ always implies a dramatic reduction in the useful life of the valve.
Iam pretty sure run an tube amp as a test tube device is a dangerous situation, as a new tube may damaged the amp or even made a fire.
Insert a untested new tube in a amp is a risky act.
My tubes dont had baquelite base, 6C33 usually run over 200ºC in regular use, so baking is not a prob.
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I dont want cryogenics anything, I nor even talk on it.
I am ask info on baking tubes.
the best thing to do then is to just get a tube that you need not bake in the oven, too much trouble for so little gain...
Induction works initially because the getter ring forms a shorted antenna to the RF energy. Since the barium getter is in the ring, it gets ballistically heated. Repeating the inductive heating after the fact will still heat the ring, but the barium is now on the glass, so any effect would most likely be negligible, IMO.
The theory is that you want the residual gas to be soaked up by the getter without having to heat the cathode to a normal working temperature, and without drawing any current. Residual gas can attack the cathode, but this effect is greatest when the cathode is fully heated. If you simply switch on an old valve and use it for a while, it is possible that you are ionising the gas and allowing it to attack the cathode before the getter has had much chance to do anything. In the oven, however, you can heat everything to a couple of hundred degrees (normal working temp) so the getter can do its job, but the cathode is no hotter than anything else.
Whether it is truly an effective treatment, I don't know.
There is no real evidence to support this.
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Furthermore, any gas will be adsorbed very fast by all the metal structures in the tube. These molecules are "glued" on the solid's surface or even get transported in the first atom layers and gaps and defects.
Any old Telefunken/RCA/etc. engineer must be turning in their graves when they read this
Any old Telefunken/RCA/etc. engineer must be turning in their graves when they read this
If this would be true, life would be so much easier in the lab. We wouldn't need expensive vacuum pumps, baking large machines at 200°C for days and the like - great!
Think about it again, and maybe read one or two books on vacuum technology. I had to and I did - designing, building and operating UHV systems for roughly 7 years now.
Some gas gets adsorbed at the inner surfaces of a vacuum vessel, but at non-zero temperatures you get some balance between adsorption and desorption, which results in residual gas pressures inacceptable for high or even ultra-high vacuum systems. If you really want UHV conditions, you have to bake the whole apparatus to desorb the gas from the inner surfaces, pump it away and then let the apparatus cool down. But even after that, you need pumps to keep the good pressure, as still some residual gas desorbs from the surfaces.
In a vacuum tube, this pumping is done by the getter layer on the glass. As someone already said, the reaction rate rises with temperature (rule of thumb: reaction rate doubles for 10°C increase). Heating a tube will help to clear residual gas. I don't see why this shouldn't be done using the tube heaters instead of an oven...
Residual gas being trapped on or even beneath the surface atoms happens only with a few metals (which are then used as getters) or by helping the process with some high voltage, as in ion getter pumps. In those, residual gas gets ionized, the ions are accelerated towards a getter surface and then 'buried' inside due to their momentum. But this won't happen without some help, as you claimed.
Regards,
Andreas
"
In a vacuum tube, this pumping is done by the getter layer on the glass. As someone already said, the reaction rate rises with temperature (rule of thumb: reaction rate doubles for 10°C increase). Heating a tube will help to clear residual gas. I don't see why this shouldn't be done using the tube heaters instead of an oven...
Residual gas being trapped on or even beneath the surface atoms happens only with a few metals (which are then used as getters) or by helping the process with some high voltage, as in ion getter pumps. In those, residual gas gets ionized, the ions are accelerated towards a getter surface and then 'buried' inside due to their momentum. But this won't happen without some help, as you claimed.
Regards,
Andreas"
My point entirely!
In a vacuum tube, this pumping is done by the getter layer on the glass. As someone already said, the reaction rate rises with temperature (rule of thumb: reaction rate doubles for 10°C increase). Heating a tube will help to clear residual gas. I don't see why this shouldn't be done using the tube heaters instead of an oven...
Residual gas being trapped on or even beneath the surface atoms happens only with a few metals (which are then used as getters) or by helping the process with some high voltage, as in ion getter pumps. In those, residual gas gets ionized, the ions are accelerated towards a getter surface and then 'buried' inside due to their momentum. But this won't happen without some help, as you claimed.
Regards,
Andreas"
My point entirely!
The metal parts in a valve are frequently the source of the gas, which evolves out over time!
I have never tried baking a valve, but Merlin's explanation makes sense to me. Heating both releases adsorbed gas from the internal metalwork (physics) and encourages the getter to soak it up (chemistry), while at the same time protecting the cathode from ion bombardment which could happen with a gassy valve in normal use.
People dragging in cryo-treatment are merely showing that they are not following the plot of this thread. Cryo, if it does anything at all, is about treating the metal not removing the gas.
People dragging in cryo-treatment are merely showing that they are not following the plot of this thread. Cryo, if it does anything at all, is about treating the metal not removing the gas.
Iam new on this subject, but seems the metal absorbing gass you mention is the metal donut getter as used in 300B and big triodes.Furthermore, any gas will be adsorbed very fast by all the metal structures in the tube. These molecules are "glued" on the solid's surface or even get transported in the first atom layers and gaps and defects.
Any old Telefunken/RCA/etc. engineer must be turning in their graves when they read this
I unknow steel metals that sinking air in a semi-vaccum tube condition(which looks as corrosion), hence the need for getters that these engineers put inside every tube.
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Powering any cold tube with the high voltage B+ always implies a dramatic reduction in the useful life of the valve.
There is no real evidence to support this.
It depends on the personal experience on tubes or further reading on Google.
But it is easy presume that a valve that receives hundreds of Volts just 5 seconds after power on will had a short life, or worst may ended his life in a unexpected or catastrophic way.
When most amps with a big triode output tube(usually 900V on the plate) lasts only 500 to 1000hours means it dont had enough delay to heat the cathode and receive the HV just after the amp power on, ie the tube is cold yet.
Popular Pentodes(EL34,6550,KT88) that last only 2 to 3K hours also are in this condition, they receive the HV with the tube cold.
All these amps had just one power on switch, obviously this sole switch started both, the cathode heating and the hi voltage B+ at the same time.
The only brand I aware had two power on switches are Atma-Sphere amps, one for heating the cathode and after some minutes the second switch must be pressed for delivery the HV.
How much minutes Ralph recommend to press the second switch I would like to know.
Applying high voltage and heating simultaneously does no harm unless the voltage is rather high. Normal domestic amplifiers and most instrument amplifiers do not need sequenced switching; it could even be harmful. High power PA and valve transmitters do need proper sequencing, because of the high voltages they use; in this case they will probably have sequencing built in, as it is unreasonable and error-prone to expect the user to get the timing right every time.
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