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Old 23rd February 2011, 03:13 PM   #1
alejo is offline alejo  Argentina
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Default what I need for safe use mercury rectifier

Hello I build in last years lots of tubes amps. and always use 5u4, 5y3, az41, etc for rectifier.
Never use mercury rectifier because iŽread out there in the web, "mercury rectifier is very dangerous"

Today IŽfind NOS Philips AX50 mercury rectifier; and my question is:

_Why is more dangerous than 5u4g? (iŽnow mercury, but why?)

_what I need for safe use mercury tube?

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Old 23rd February 2011, 03:17 PM   #2
DF96 is offline DF96  England
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I am not an expert, but I suggest:
1. never break it, as mercury vapour is poisonous.
2. shield the UV it emits when operating.
3. read the datasheet and obey any warnings and limitations.
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Old 23rd February 2011, 04:47 PM   #3
Knarf is offline Knarf  Denmark
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You don't want to use Mercury vapor rectifiers, even if you think you do. Using them for audio is dumb. They are in my view the hallmark and signature of inexperience.

True, they emit a pretty blue glow, but they are really, Really, *REALLY* noisy rectifiers. They make enough noise that back in the day you could literally hear in your AM broadcast radio receiver if the radio amateur next door keyed his Morse code transmitter. The Mercury vapor rectifiers acts as wide band audio and RF noise generators when they are conducting. This is not switching noise, it happens even if they only conduct DC.

That said, if you insist, then:

*) Mercury vapor rectifier tubes cannot really take high peak currents when used as AC rectifiers. So you usually use them in choke input filters. Any input capacitor in cap input filters needs to be really small, on the order of a few uF. The data sheet will tell you more. If it doesn't say anything, then it is assumed you will only use choke input.

*) They need a pre-heating time. Meaning you apply heater power to the rectifiers for several minutes before you apply the high AC voltage. This is to allow the Mercury inside the rectifiers time to fully evaporate before switching on. Doubly important if the tubes has been moved or shaken since last time they had power applied.

*) When hot the tubes contains a fair amount of Mercury vapor. As opposed to ordinary, liquid Mercury at room temperature this stuff is fairly nasty. If you accidentally break a rectifier while power is applied, the vapor will immediately disperse in your living room. It will be impossible to avoid inhaling some of it, or prevent getting Mercury all over the place. So condemn your house, and build a new one. Much safer for your family that way. Check symptoms for Mercury poisoning, they are quite entertaining.

*) When Silicon rectifiers of reasonable voltage rating was introduced, there was a stampede of radio amateurs away from Mercury rectifiers. With good reason I'd say.

Sorry to be the bringer of bad news. However I'd rather say this now before you build anything with them, and then post photos, asking for comments.
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Old 23rd February 2011, 04:49 PM   #4
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MV rectifiers need to be preheated before the high voltage is applied. Allow up to 1 min with just the filament voltage until the mercury is vaporized. Then apply HV.

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Old 23rd February 2011, 05:02 PM   #5
kevinkr is offline kevinkr  United States
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The biggest problems of all are when one inadvertently gets broken, there is sufficient elemental mercury in a cold tube to constitute a significant environmental and hence health hazard. Clean up depending on the surface it spills on can be problematic, in any event it is usually recommended that a local hazzmat specialist do the clean up. There are recommended clean up procedures for fluorescent lamps which generally contain a lot less mercury afaik.

The worst case scenario might be if an operating tube got broken and the vapor escaped because it will quickly condense leaving micro-droplets of mercury on everything it touches.

I was given a bunch of 866 rectifiers, I don't plan to use them, in fact I will return them at some point to the original owner.

The two things I try to avoid having in my house are MV rectifiers and PCB filled oil caps..
"To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine
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Old 23rd February 2011, 06:56 PM   #6
Alkis is offline Alkis  Greece
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I was thinking of using Mercury rectifiers when I came accross with this thread.There is no safe use with MVRs
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Old 25th February 2011, 02:54 PM   #7
alejo is offline alejo  Argentina
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This confirms my suspicions, it is very dangerous for me. I will not use them. thank you all for your responses.

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Old 25th February 2011, 08:42 PM   #8
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The only thing that Hg diodes have going for them is glowey bottle kewelness. Back in "the day", they were used for applications requiring high PRV, high currents, and superior voltage regulation. These days, all of this is available with silicon that does not require another hole in the chassis, a special, low voltage, high current, and insulated to stand up to 10KV filament xfmr.

Like the OP explained, Hg diodes are liable to RF parasitics (since it's a glow discharge, it has negative resistance) require preheating (~30 secs if the Hg hasn't been disturbed since last power down, ~30mins if it has -- otherwise poofage due to having Hg droplets bridging the anode and cathode is a distinct possibility). Too much bother.

One thing that you don't have to worry about is UV, since glass is opaque to UV (only fused quartz is transparent to UV, and is standard for UV sources).

If you just have to have that glowey bottle goodness, look into substituting xenon diodes for the Hg vapor variety. You will still have to deal with that RF parasitic problem, however.

Personally, I'd say t'hellwiddit. If you can't do it with vacuum diode(s) you're better off going Si instead.
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Old 26th February 2011, 06:16 AM   #9
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Reports of the danger and RF hash of MV rectifiers are exagerating. Of course one should be extremely careful not to break the glass as mercury is hazardous. I remember the times when mercury was common in thermometers. I remeber these things also falling on the floor and the mercury beeing spilled. I even saw this happen in a hospital once. No clean up team had to come to remove the spill. And the people vitnessing this are still alive

Also many people claim MV tubes provide much better sound than vacuum rectifiers.

I used 866As a lot. RF is not really an issue in a well laid out PSU.

I wrote about a 866A PSU here:

VinylSavor: Single Ended Amplifier Concept, Part 5

Best regards

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Old 26th February 2011, 07:38 AM   #10
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there's an important difference between breaking an MV rectifier or a Hg thermometer... In the former case, the Hg is vaporized! It would spread around the room in litterally seconds. People would need to hold their breath and clear the house immediately and then wait outside for hours or days until all the vapor has deposited on surfaces (which then need to be cleaned ). In the latter case, the droplets can just be collected on a piece of paper and discarded. Liquid mercury would only release some vapor when left lying on the floor for weeks. Remember you could drink a thermometer and not get poisoned; the vapour reaching the lungs is where poisoning takes place.

Tip: a rather cool looking high-vacuum diode with high PIV, cheap too, is the U19/CV187...

Never send a human to do a machine's job. --Agent Smith
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