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Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
Wow. Really nice Kizmo. Where/how did you get it?
Zb wrote ...
Nice! Just one thing I noticed: The name plate says it's manufactured in 1976... it might have PCBs
PCBs supposedly not that toxic. It shouldn't do anything to your hand if you were to stick it in the oil. It's just not a very good idea Just don't burn it, spill it or anything. You could get a PCB tester to see if it had PCBs. I don't know what you should do if you found it to have PCBs. I would take a guess and fill it with oil that didn't contain PCBs although that could get expensive.
Registered Member #1497
Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801
You can test for PCB oil a few ways:
1. Take a container of water, and drop a few drops of the oil in. Regular oil floats PCBs will SINK to the bottom Remember to get rid of the container, clearly, don't drink from it... 2. Carefully burn the oil, PCBs will burn with a smoky flame due to being highly aromatic and substituted with chlorines.
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
I set up my 872A just to see what the glow looked like in real life. I used a rewound MOT for the filament. I used a 25V transformer and a 200W lamp connected to the plate and the filament (I wasn't sure if I needed it but I just put it there for safety). The glow appears brighter in the pictures than in real life. What might be causing the glow above the anode? There shouldn't be much current flowing (if at all) in that region of the tube.
Registered Member #397
Joined: Wed Apr 19 2006, 12:56AM
Location: Western Washington
Posts: 125
Hey an 872A! I just bought a few for project in progress.
[edit, just realized you applied 25V to the anode, not the filament, whew!]
Did you follow typical procedure for firing up a mercury vapor rectifier? Mercury rectifier tubes are not as easy going as normal rectifier tubes and require some kid gloves and procedural prepping, as well as stable temperatures that aren't too hot or too cold. It looks like the mercury in your tube hasn't even vaporized completely yet. I can see tons clinging to the wall up top. Its probably stuck all over the anode plate and the walls, hence why it's got funky glowing distribution.
This is a factory precautionary prep sheet that was in the box that my NOS Sylvania 866A came in:
Mercury condensation
Insure that all mercury, which during shipment has become lodged within the tube elements and in the upper bulb region, is distilled to the lower section of the tube before applying anode voltage. The procedure recommended to so "condition" the tube is as follows:
1. Invert the tube in such a manner as to release any mercury trapped in the anode, grid, or cathode structures. Then slowly return the tube to an upright position.
2. Tap the tube lightly to release any large globules of mercury hanging on the bulb walls.
3. Apply filament voltage only and allow the tube to heat until all mercury has been completely distilled from the top of the tube as indicated by the disappearance of the silver coating inside the bulb. The time necessary to accomplish will range from 15 to 90 minutes, depending on the tube and the conditions of ventilation. The time can be greatly reduced by temporarily covering the top of the tube with a cloth blanket.
4. Once the tube has been conditioned as described above, no further treatment is needed unless the tube is removed from the socket and inverted.. To eliminate delay in replacing tubes, it is well to have one or more spares which have been previously conditioned and carefully stored in an upright position.
Anode voltage
Where practical, it is advisable to "break in" a new tube by gradually increasing the applied anode voltage. If no voltage adjustment is available, starting the tube at reduced current is recommended.
Most equipments are provided with a time delay relay to insure that filament heating time is observed. In no instance, however, should anode voltage be applied until the condensed mercury temperature, measured at the location indicated on the tube data sheet, is above the minimum allowable condensed mercury temperature. This requirement is particularly important when it is necessary to start operation at low temperatures as the mercury heating time may greatly exceed the cathode heating time provided by the time delay relay.
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
Ah, I didn't know about the part that all of the mercury has to be vaporized. I did have a fan blowing air on one side to cool it so more mercury condensed on that side (the left side in the pictures). I did let the tube warm up for 30-45 seconds before applying any plate voltage though. I don't plan to do much with this tube yet. I just turned it on to see the glow and take a couple pictures of it. Thanks for finding that information. I'll condition it when I find a use for it.
EDIT: "Although low-pressure mercury arcs (all tubes presented here work at internal pressures below athmospheric pressure) emit most of their radiation in the short ultra violet-range (254 nm, the "typical" Hg-line), the visible blue light being only the smallest part of the emitted spectrum, there is - as far as we know today - hardly any danger from this radiation: The glass bulbs absorb this part of the spectrum the stronger the shorter the radiation wavelength will get, so there will almost nothing of the dangerous radiation (below 300 nm wavelength - its energy being limited by the voltage drop - about 15 eV max) come out of the tube. The short-UV-dose you get at each thunderstorm lightning you look at is much higher!"
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