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Registered Member #223
Joined: Mon Feb 20 2006, 06:42PM
Location: Ottawa, Ontario, Canada
Posts: 125
Well I found this old rectifier in my junk box. It’s probably been there for ages.. In fact I don't even remember where I got it. Date of manufacture was 1971! I thought maybe I should test it to see weather or not it still works. I had to solder a wire to the bit of wire that was left from the top terminal since the cap broke off of the tube. I then wound a filament transformer out of an old 120 to 12v toroidal transformer. I set it up to half-waves rectify mains which is then fed into a 100w light bulb. I applied power and after 10 seconds of warm up the light bulb came on but at half the regular output. (as expected). I haven't been able to locate a data sheet but I was just wondering if this could actually be useful for anything? I really doubt it. What kind of voltage and current are these things usually rated for? I googled mercury vapor rectifier and I seem to only get information about mercury ark rectifiers. Maybe I could use it in a voltage doubler for my VTTC so that it stays with the spirit of being a tube coil instead of using solid state diodes.
Also one thing I noticed was that there is a loose peace of glass like object rattleing inside of the tube.. I have looked high and low and can't see where it could have come off of inside .. Is this something that is supposed to be in there?
Here is a picture of the rectifier supplying a 100w light bulb:
Registered Member #290
Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673
Hi Dan
Cool picture, just remember that these are not very efficient and you may lose a few volts. Also in my old transmitter I used in the 60’s had a flash over and it was not very nice to my finals……
Registered Member #223
Joined: Mon Feb 20 2006, 06:42PM
Location: Ottawa, Ontario, Canada
Posts: 125
Well after some searching I managed to find a datasheet for this 8008 rectifier. It only said that it was and equvilant to an 872A (Data Sheet). Apparently it is rated for 1.25A rms, 5A peak, and 50A fault. However I'm confused about the voltage rating.. It says 5,000V for 20C to 60C condensed mercury temprature and 10,000 V for 20C to 70C condensed mercury temprature. Is this a typo or something? It would seem however that they are sensitive to temrature though.
It looks like I can still use it in my VTTC once I get a new mot. (Killed my old one trying to remove the shunts ) I am currently using a magnetron with it's magnets removed as the level shifter diode. However it can only process a few hundread milliamps. One thing that I am conserned about though is that my VTTC puts out a rather strong RF feild which seems to be able to ionize the mercury vapor inside the tube. Willl this affect it's operation as a rectifier?
I was expecting this rectifier to be able to handle way more current. I mean this thing is huge and it is only rated for 1A at 5,000V. I mean 5 1n4007 could do that and it wouldn't they wouldn't be running at a billion degrees C.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Hi Dan
I have a couple of mercury vapour rectifiers here and they are very low powered for their size. The small one is about 9" tall and handles 1.25A at 8kV, the big one is 12" and handles 4A. I started a thread about them on the old board:
They are temperature sensitive, because the mercury vapour pressure varies with temperature and the breakdown voltage depends on the pressure. As for RF ionization: I tried mine on top of a Tesla coil but couldn't get anything beyond some faint green-yellow glowing patches on the cathode sleeve.
You're right about the string of 1N4007s. There is still old tube equipment with mercury vapour rectifiers in service, and I heard you can get "upgrades" that consist of the old dead rectifier tubes cracked open, the guts replaced by a string of silicon diodes, and the bottle packed full of sand for insulation and stuck back together.
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