Thomas
A gassy tube can draw excessive current. In the case of an 80 or other rectifier, can arc over and burn up the power transformer. This might be what John meant?
Norm
:Just wondering how a gassy tube could be a fire hazard. I have never heard of this before.
:
:Thomas
T.D.
Isn't there a solid-state replacement that can be used in place of the 80? I know it would diminish the value of the radio, but it would certainly be better than dealing with a gassy tube, don't you think?
:Hi Thomas
:
: A gassy tube can draw excessive current. In the case of an 80 or other rectifier, can arc over and burn up the power transformer. This might be what John meant?
:
:Norm
:
::Just wondering how a gassy tube could be a fire hazard. I have never heard of this before.
::
::Thomas
:I had this experience recently for the first time in an Atwater Kent 60C. Luckily, I had an unused 80 that was probably a later version that combined two 5Y3's together.
:
:Isn't there a solid-state replacement that can be used in place of the 80? I know it would diminish the value of the radio, but it would certainly be better than dealing with a gassy tube, don't you think?
:
::Hi Thomas
::
:: A gassy tube can draw excessive current. In the case of an 80 or other rectifier, can arc over and burn up the power transformer. This might be what John meant?
::
::Norm
::
:::Just wondering how a gassy tube could be a fire hazard. I have never heard of this before.
:::
:::Thomas
As for the problem with 80 tubes vs. solid state, tubes do not often get gassy. Just use them and enjoy. Don't worry about things too much. People worry about stuff a lot. Solid state diodes can short and leak backwards. This can destroy components as well (electrolytics). Any way you go in life, you are going to take a risk. Tubes are great, and they don't usually blow up power supplies. I've never seen this happen personally, though it almost happened once, but I was using a gassy tube in the first place. I've seen the power supply blow a tube. Tubes usually get gassy from sitting cold (using them usually burns up any traces of gas). Sometimes gas can be released by overheating a tube, as this process is normally used to release gas during evacuation. When the bulb is closed, the gas stays inside.
Gotta go.
T.
hi i think this is related i have 6 or 8 6v6 tubes that have a whte coating on the top i have at least that many more in the same bunch that are clear i assumed that these wre shot they were nos tubes but had been laying outside for a long time when i got them i never had any use for 6v6s so i never tested them but wonder what causes this or were they made that way? butch
When the tube is evacuated, small traces of oxygen and other gasses remain in the tube. These traces are not those which can easily be counted, but are microscopic. There are also traces of gasses in the various components in the tube either in gas or chemical form (compound). The gasses, in chemical compound form with the various components (metal), may be released at a later point in time if the tube is overheated. To eliminate the gasses in gas form, whether they currently exist or will be released for some reason at a later point in time, the getter, a metallic type of substance that oxidizes easily, is placed inside the tube. The tubes with the ring, either in circuilar or D shape, have the getter dispursed by heating the ring with high intensity RF waves. Like a transformer or radio transmitter, a special device radiates RF waves at the ring. This is done at the tube factory, and is done after the tube has been evacuated and closed. Currents are induced in the ring from the RF waves, and the ring heats up. As you can see, the ring is hollow or U shaped like a trough. The getter chemical rests in this trough. When the ring heats up, the getter vaporizes and is dispursed onto the glass and temporarily throughout that area of the tube until it all condenses onto the glass. With the older tubes that have the solid piece of metal, also often shaped like a D, the dimple in the middle holds the getter. I am not sure how this metal piece is heated. I think it is simply heated when the tube is cooked. In either case the tube is cooked when initially evacuated, both for testing purposes (strength, etc.), and also to cook off impurities and to drive trapped gasses out of the glass and elements.
The getter, as you see it in a new tube, is silver. Older tubes have a bright silver getter, and newer tubes have a more brownish getter. The more modern getter is far more reactive, and because of that is probably far superior. I have broken old tubes by accident, and the bright silver getter (formed off of the solid D metal piece) took months to oxidize. The getter in modern tubes, when they are broken, turns white almost instantly. Its transformation from metallic to white is the physical change that takes place when the chemical oxidation takes place (gasses combine with the metal). Tubes that you own that have white getters may or may not be bad. If trapped gas within the tube suddenly was released for one reason or another and the getter chemically combined with it so that it was no longer a gas (a gas would interfere with electron function within the tube), if all of the gas was absorbed, the tube would likely function well. If the getter was not able to absorb all of the gas (the getter was used up before all of the gas was absorbed), then the tube would be faulty. If the tube is obviously cracked, then it is surely faulty. You can find tubes where some of the getter has oxidized. This does not mean that the tube is bad. Testing it will tell for sure. This does not mean that the tube will have a short or long life, either. Only using it will tell for sure. I have a kinescope made by DuMont, a very fine one to be sure (brilliant picture), in which there are no traces of getter on the glass really, just a faint haze above the getter rings that is barely visible. Still, as I said before, this tube functions perfectly. I don't know if this tube ever did have getter silvering on the glass.
Testing your tubes will tell you for sure if they are usable or not. Ideally a tube should have a shiny, healthy getter. One interesting phenomenon you may notice is that a tube which has lost its vacuum cannot be lit at its appropriate filament voltage. You can light the filament by applying a higher voltage. You will also notice that when this voltage is disconnected, the filament cools extremely quickly. The reason for this is because since there is now air in the tube, the heat of the filament is carried away too quickly for it to light at its designated voltage. This is also why it cools so quickly. When the filament is in a vacuum, heat is not drawn off of it quickly at all. Thus less voltage is required to light it. Furthermore, since the heat is not pulled away quickly, it stays glowing for a long period after current has been disconnected.
Thomas
The ionized gas is sometimes gas the has found a way into a tube, or boiled out of some material within the tube. If you know how HID lamps operate, it is a miniature version of that often caused by AC current being applied to rectifiers. This is why it sometimes takes a while for a gassy tube to reveal itself.
As for getter material, usually a Barium compound, even though a tube gets evacuated quite completely, it is not perfect. The silvery flashing on the side of the tube is usually the flash from the getter to bind up the remaining gas molecules. When a tube has lost it's seal, Barium is very reactive to a number of gasses in the atmosphere and becomes an oxide of barium and turn white. INside of a good vacuum tube, there are not enough gas molecules to react all of the Barium normally. The white material on the heater and the cathode sleeve are aany of a few compounds of "Alkaline Earths" as RCA calls them, most are salts of Thorium which has/have good electron emissive abilities at modest heats.
:Well, if you ever find a use for 6V6 tubes, they are great tubes. They have a wonderful sound. The white substance is getter. I do not fully understand what chemicals were used for the different getters, as there were different types, but here's the purpose:
:
:When the tube is evacuated, small traces of oxygen and other gasses remain in the tube. These traces are not those which can easily be counted, but are microscopic. There are also traces of gasses in the various components in the tube either in gas or chemical form (compound). The gasses, in chemical compound form with the various components (metal), may be released at a later point in time if the tube is overheated. To eliminate the gasses in gas form, whether they currently exist or will be released for some reason at a later point in time, the getter, a metallic type of substance that oxidizes easily, is placed inside the tube. The tubes with the ring, either in circuilar or D shape, have the getter dispursed by heating the ring with high intensity RF waves. Like a transformer or radio transmitter, a special device radiates RF waves at the ring. This is done at the tube factory, and is done after the tube has been evacuated and closed. Currents are induced in the ring from the RF waves, and the ring heats up. As you can see, the ring is hollow or U shaped like a trough. The getter chemical rests in this trough. When the ring heats up, the getter vaporizes and is dispursed onto the glass and temporarily throughout that area of the tube until it all condenses onto the glass. With the older tubes that have the solid piece of metal, also often shaped like a D, the dimple in the middle holds the getter. I am not sure how this metal piece is heated. I think it is simply heated when the tube is cooked. In either case the tube is cooked when initially evacuated, both for testing purposes (strength, etc.), and also to cook off impurities and to drive trapped gasses out of the glass and elements.
:
:The getter, as you see it in a new tube, is silver. Older tubes have a bright silver getter, and newer tubes have a more brownish getter. The more modern getter is far more reactive, and because of that is probably far superior. I have broken old tubes by accident, and the bright silver getter (formed off of the solid D metal piece) took months to oxidize. The getter in modern tubes, when they are broken, turns white almost instantly. Its transformation from metallic to white is the physical change that takes place when the chemical oxidation takes place (gasses combine with the metal). Tubes that you own that have white getters may or may not be bad. If trapped gas within the tube suddenly was released for one reason or another and the getter chemically combined with it so that it was no longer a gas (a gas would interfere with electron function within the tube), if all of the gas was absorbed, the tube would likely function well. If the getter was not able to absorb all of the gas (the getter was used up before all of the gas was absorbed), then the tube would be faulty. If the tube is obviously cracked, then it is surely faulty. You can find tubes where some of the getter has oxidized. This does not mean that the tube is bad. Testing it will tell for sure. This does not mean that the tube will have a short or long life, either. Only using it will tell for sure. I have a kinescope made by DuMont, a very fine one to be sure (brilliant picture), in which there are no traces of getter on the glass really, just a faint haze above the getter rings that is barely visible. Still, as I said before, this tube functions perfectly. I don't know if this tube ever did have getter silvering on the glass.
:
:Testing your tubes will tell you for sure if they are usable or not. Ideally a tube should have a shiny, healthy getter. One interesting phenomenon you may notice is that a tube which has lost its vacuum cannot be lit at its appropriate filament voltage. You can light the filament by applying a higher voltage. You will also notice that when this voltage is disconnected, the filament cools extremely quickly. The reason for this is because since there is now air in the tube, the heat of the filament is carried away too quickly for it to light at its designated voltage. This is also why it cools so quickly. When the filament is in a vacuum, heat is not drawn off of it quickly at all. Thus less voltage is required to light it. Furthermore, since the heat is not pulled away quickly, it stays glowing for a long period after current has been disconnected.
:
:Thomas
:Norm hit the answer- excessive current draw. I know of one instance where this destroyed a "transformerless" radio (not one of mine), and looking at how it was made the results could have been far worse. On a transformer type, yes there is a margin of safety, but how readily are you going to walk into the shops downtown and buy a direct replacement off the shelf?
:
:The ionized gas is sometimes gas the has found a way into a tube, or boiled out of some material within the tube. If you know how HID lamps operate, it is a miniature version of that often caused by AC current being applied to rectifiers. This is why it sometimes takes a while for a gassy tube to reveal itself.
:
:As for getter material, usually a Barium compound, even though a tube gets evacuated quite completely, it is not perfect. The silvery flashing on the side of the tube is usually the flash from the getter to bind up the remaining gas molecules. When a tube has lost it's seal, Barium is very reactive to a number of gasses in the atmosphere and becomes an oxide of barium and turn white. INside of a good vacuum tube, there are not enough gas molecules to react all of the Barium normally. The white material on the heater and the cathode sleeve are aany of a few compounds of "Alkaline Earths" as RCA calls them, most are salts of Thorium which has/have good electron emissive abilities at modest heats.
:
:
:
::Well, if you ever find a use for 6V6 tubes, they are great tubes. They have a wonderful sound. The white substance is getter. I do not fully understand what chemicals were used for the different getters, as there were different types, but here's the purpose:
::
::When the tube is evacuated, small traces of oxygen and other gasses remain in the tube. These traces are not those which can easily be counted, but are microscopic. There are also traces of gasses in the various components in the tube either in gas or chemical form (compound). The gasses, in chemical compound form with the various components (metal), may be released at a later point in time if the tube is overheated. To eliminate the gasses in gas form, whether they currently exist or will be released for some reason at a later point in time, the getter, a metallic type of substance that oxidizes easily, is placed inside the tube. The tubes with the ring, either in circuilar or D shape, have the getter dispursed by heating the ring with high intensity RF waves. Like a transformer or radio transmitter, a special device radiates RF waves at the ring. This is done at the tube factory, and is done after the tube has been evacuated and closed. Currents are induced in the ring from the RF waves, and the ring heats up. As you can see, the ring is hollow or U shaped like a trough. The getter chemical rests in this trough. When the ring heats up, the getter vaporizes and is dispursed onto the glass and temporarily throughout that area of the tube until it all condenses onto the glass. With the older tubes that have the solid piece of metal, also often shaped like a D, the dimple in the middle holds the getter. I am not sure how this metal piece is heated. I think it is simply heated when the tube is cooked. In either case the tube is cooked when initially evacuated, both for testing purposes (strength, etc.), and also to cook off impurities and to drive trapped gasses out of the glass and elements.
::
::The getter, as you see it in a new tube, is silver. Older tubes have a bright silver getter, and newer tubes have a more brownish getter. The more modern getter is far more reactive, and because of that is probably far superior. I have broken old tubes by accident, and the bright silver getter (formed off of the solid D metal piece) took months to oxidize. The getter in modern tubes, when they are broken, turns white almost instantly. Its transformation from metallic to white is the physical change that takes place when the chemical oxidation takes place (gasses combine with the metal). Tubes that you own that have white getters may or may not be bad. If trapped gas within the tube suddenly was released for one reason or another and the getter chemically combined with it so that it was no longer a gas (a gas would interfere with electron function within the tube), if all of the gas was absorbed, the tube would likely function well. If the getter was not able to absorb all of the gas (the getter was used up before all of the gas was absorbed), then the tube would be faulty. If the tube is obviously cracked, then it is surely faulty. You can find tubes where some of the getter has oxidized. This does not mean that the tube is bad. Testing it will tell for sure. This does not mean that the tube will have a short or long life, either. Only using it will tell for sure. I have a kinescope made by DuMont, a very fine one to be sure (brilliant picture), in which there are no traces of getter on the glass really, just a faint haze above the getter rings that is barely visible. Still, as I said before, this tube functions perfectly. I don't know if this tube ever did have getter silvering on the glass.
::
::Testing your tubes will tell you for sure if they are usable or not. Ideally a tube should have a shiny, healthy getter. One interesting phenomenon you may notice is that a tube which has lost its vacuum cannot be lit at its appropriate filament voltage. You can light the filament by applying a higher voltage. You will also notice that when this voltage is disconnected, the filament cools extremely quickly. The reason for this is because since there is now air in the tube, the heat of the filament is carried away too quickly for it to light at its designated voltage. This is also why it cools so quickly. When the filament is in a vacuum, heat is not drawn off of it quickly at all. Thus less voltage is required to light it. Furthermore, since the heat is not pulled away quickly, it stays glowing for a long period after current has been disconnected.
::
::Thomas