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Mercury rectifiers

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Hello everybody.
I'm building an EL 34 SE amp and I would like to use the
866A mercury diodes. I saw them supplying a 212 about 1kV
(I think). Anyway, I need only about 330V, so, my questions are:
-may I use it?
-how? (I'm a neophyte...)
-Did someone ever try them? How about the sound?

Suggestions, advices, insults, money, food(Ha!) are welcome.

Many Thanx, gimpus.

[Edited by gimpus on 04-21-2001 at 11:13 AM]
Like Lisandro, I thought mercury tubes were over the horizon. (And this from a guy who has confessed to a love of tubes on a primarily SS site...and endured the backlash therefrom.) However, that said, you've brought an interesting idea to the table. I might have to look up those tubes.
And yes, they're pretty sexy looking with the blue glow.
Now the $10,000 question is...how do they sound?
I'm afraid a single-ended triode amp wouldn't be practical for me, as my mids and tweeters are in the upper 80's as far as efficiency and, unfortunately, I've never heard a horn speaker I could live with, as their colorations are beyond what I consider to be high-end. (I readily concede their efficiency and dynamics, however.) Still, for those who value dynamics above other characteristics, I can see the temptation.
Single-ended amps are not hard to build. I'd say go for it if your speakers will jump to the beat of a (comparatively) low-powered amp. My recommendation would be to get in contact with the fellow who built those amps and find out who made the tubes (Sovtek, Svetlana, NOS, etc.). If they're in current production, you should be able to get specs and such from the manufacturer, possibly even suggested circuits. If they're not in current production, I'd be wary of using them.
Let me know how it sounds.

Actually, mercury rectifiers are suposed to be VERY good (in terms of power, speed, etc)... why does low pressure mercury fumes work as a semiconductor, beats me. Again, are you sure you can find those easily? As i know, nowadays they're used only when needed to rectify HIGH powers, and even then, they're custom designed.

But yes, they do look lovely :D I once wanted to add a display to my future amp using Nixies, but they're difficult rare to get here.
Hello, been reading your discussion about Mercury rectifiers. I allso like those gloin' babies quite a bit, but, they are a bit tricky to use. I'm building a Phono pre-amp, and have aquired a RCA-82 rectifier to do the job. It is very cool, but as most MR, it don't accept ANY capacitor at the filter input, thus a Choke filter must be used. This forcing me to use a bigger transformer. Not really a bad thing, but a little more expencive:) Further, They have to reach a certian working temperature before the High Voltage is connected, or else the rectifier is prob. destroyed. This must be done either by a relay, or with some small resistors in series with the plates.
Other devices using gas is the VR series of 0A2, 0C3 etc. They glow PURPLE! Extremely cool!
Mercury vapor tubes were very common in projection equipment in movie theatres back into the 50's. Huge mercury vapor tuber were in use in the 20's through the 30's in some locations for rectification for arc lamps. These tubes were huge and some were close to 3 feet tall. There was a mechanism that tipped the tube slightly when they were switched on to help what mercury was in solid form to turn to vapor. Each rectifier cabinet was the size of a refrigerator. Tungar tubes were also used alot as well. I'm not sure what the difference is between a tungar and a mercury vapor rectifier but they seem to operate the same way.
I was at a theatre doing service work last week in Ontario Oregon and they were still using an old Motiograph Tungar rectifier unit for exciter lamp power in the sound reproducers....the theatre owner said that the particuluar pair of tungars was well over 10 years old and still going strong! He still had another new pair......Sort of like the eveready bunny lives up there!
Needless to say this theatre WAS NOT equipped with Dolby Digital or THX of any sort, although there was a poor mans stereo system there.
Mark Gulbrandsen
General Theatrical Supply
Salt Lake City, UT
The idea with mercury rectifiers (such as the 866A) is that the electrons that are flowing from the filament to the anode (erm, "plate" for the Yanks) collide with mercury gas (this gas is created by the filament's heat which evaporates the liquid Hg). The gas mollecules are hit with these high-velocity electrons - in the process knocking additional electrons off the Hg atom. The Hg atom therefore becomes a + ion since it has lost electrons, and moves to the cathode, whilst the electrons removed from it flow to the anode.

The point being that the Hg atoms enhance the current flow, and you can get considerably more current for a given p.d. across the tube. The 866A is good for 0.25A, I think. The ionized gas molecules are much heavier than electrons, which requires the cathode to be of heavy construction - otherwise it would get stripped by all the heavy ions hitting it.

The ionization creates a bunch of white-ish electrical noise in nearby and connected circuits, same way as 85A2, 0A2 and so forth neon tubes which use a similar principle... I could **avoid them at all cost** because of this.
If you demand tube rectification, you'll get best results with an indirectly-heated hard vacuum diode like a GZ34, GZ37 and so forth.

They are cheap because they are so obsolete, but tricky to use (you need to *always* draw enough current to keep the ionization from running out of control) and not at all worh it. Using them for aesthetic reasons is kind of ludicrous... :)
I've done a bit of research on merc-arc rectifiers myself. I also read on the web that they sound great, mainly due to the fact that they are self regulating: voltage drop is about 15V constantly. While the bible of valve circuits, the Radiotron Designers Handbook, states that voltage regulation is not required for class A amps, and therefore explicitly states that Mercury-arc rectifers should not be used because of their design conceits, there are tube gurus out there who will swear that voltage regulation is important for ultimate clarity. People on the web seem to be split on the issue. Some people have claimed that they're not so clean.

Another problem is that you have to heat the tube up before you can apply the mains voltage. That means having either some kind relay system or having two power switches... which can be a bummer.

I have yet to experiment, but I'm thinking of using one for a pre-amp project. Probably an 83 as this is a full wave tube, and therefore easier to use than the 866.
Mercury vapor rectifiers

If, perchance, you drop and break a mercury rectifier do not attempt to recover the mercury with a vacuum cleaner. You definitely don't want to aspirate fine particles of mercury. The best way of recovering spilled mercury is to just use a broom and try to sweep it all into one place.
I have a good audiobuddy who has been using mercury rectifiers for several years and the system he has built sounds fantastic.

A few points from his experience:

The ones he uses are thyratrons connected as diodes.

You must heat the filament before applying high voltage, the mercury must be ionized first or else the rectifier will be damaged.

He has not experienced the commonly mentioned problem of high frequency "hash" noise in practice.

They are extremely beautiful.

Email me and I can put you in touch with him, alternatively, make a post at Audio Asylum in the Tube DIY forum with "Mercury Rectifier" in the heading and I am 100% sure he will see it.

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