General Electric 83 plate-voltage full-wave gas rectifier

Probably the most popular of all gas-filled rectifiers, this type is the American counterpart to the European AX 50, made by Philips. Both types were used in higher-power audio amplifiers. Construction of both types is quite identical, the most striking difference (except the base) being in heater ratings: 5 V, 3 A for type 83, while 4 V and 3.75 A for the AX 50. Power ratings are up to 550 V at 250-275 mA, up to 1 A peak. System drop is constant at about 15 V. Preheating time is short, 15-30 seconds are usually (at room temperature) enough.

The gas filling consists of Mercury, which is always in an equilibrium between a condensed and a vapourised phase, even in operation. Small Mercury droplets condense at the (lower) cooler parts of the glass bulb, forming a shiny silvery coating, as you can see in the photo.

In operation, the space between cathode (V-shaped oxide-coated nickel ribbon filament) and coaxial anode is filled by a blueish-white plasma. From its construction, it is a simple direct-heated high-vacuum rectifier filled with Mercury vapour. Contrary to the AX 50, which still seems only to be available in very poor quality (at least in my experience), the 83 can still be bought in good quality from NOS ("new old stock") dealers.

Some operation requirements and safety hints applicable for all gas-filled rectifier tubes:

Preheating (the bigger and colder the tube, the longer, especially for Hg-filled tubes) is absolutely necessary, serious damage to the oxide coating will occur (erosion by heavy arcing) while applying high-voltage power if the filament is still heating up. Times are indicated in the different type descriptions. Operating Hg-tubes with reduced heating voltage will result in a non-reversible intoxication of the emissive layer, thus reducing lifetime of the tube drastically.

Generation of high-frequent (RF) noise by the arc igniting at each half-wave (what it does very rapidly, thus generating high spikes) is prohibited by inserting a small toroidal choke (1 mH or more) in series with each anode lead.

Gas rectifiers are a perfect choice for tube-HiFi-amplifiers, but changing over from high-vacuum or semiconductor rectifiers requires a very skilled technician - some startup and preheating circuitry must be added and - most probably - especially be developed first.

... and finally some important safety hints:

Don't try upgrading your amp, if you're not absolutely sure of your knowledge, experience and capabilities - serious damage to your equipment AND TO YOU - we're working here with absolutely lethal voltages - will most surely occur!!! Informations provided in these pages are absolutely NOT sufficient for this! This is no harmless hobby like playing with computers. The author of these pages will not accept any responsibilities for any damage from failed experiments.

And - never forget - Mercury is HIGHLY TOXIC! Handle your tubes as cautiously as possible! Keep them out of your children's reach! Even one broken glass bulb might contaminate a room for years! Use Zinc powder (ask at your local chemist's) to absorb liquid Mercury in case of breakage - it will form a solid alloy with only small toxicity - an Amalgam. Burnt out Mercury rectifiers - if you don't want to keep them for display - MUST BE DISPOSED OFF PROPERLY! Ask for your local disposal of fluorescent tubes - these also contain mercury.

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!