Recently I purchased some NOS mercury vacuum tubes. Straight from the factory boxes.
A journey in time. As this is my first adventure with mercury vacuum rectifiers, I wanted to be on the safe side, so I dug up some of the technical specifications for these ancient (dated 1984) tubes.
As it turns out, rightfully so.
The thing is – when you are buying from some surplus warehouse liquidation sales of ex-army stuff, there is a good chance that you shall be buying spares that the military stacked up some long long time ago, but never actually had a chance to use them.
So, basically, these 1984 dated NOS tubes, TRUE NOS tubes, that have been time warped straght into my hands in the form of brand new, unused pieces. With warranty seals on the factory boxes. The warranty has expired, by the way, some 25 years ago.
OK, So I got lucky. NOS. Never used. Virgins.
But there is a catch here … You can not just simply “TURN THEM ON” and start USING them.
( Pun intended ! )
That would actually be a very dangerous thing to do, as they would most surely short circuit inside and / or blow up in your face. And generally, you shall never ever wish to be exposed to breathing the fumes of high temperature activated mercury vapor that gets into your lungs. A painful sickness, and maybe even painful death indeed !
If, by some accident, you actually break or decompress such a rectifier tube whilst it is in operation,
RUN like HELL !!!
Passing a Window, you may consider OPENING IT (provided that the activity does not slow you running…) so that the room starts intensive ventillation immediately.
OR simply: Forget the windows and Run for your Life and the future well being of your still healthy lungs.
If you happen to break it in storage / cold conditions, this is also somewhat serious, but not critical. Just take care to very carefully collect all of the pieces and the mercury droplets onto some wipes and dispose of them as you normally would with toxic or contaminated material. Mop it up afterwards and wash your hands. Then dispose of that mop too.
So, when received the first time from the “factory” – you actually need to … format them, or pre-burn them, run them in, under controlled conditions (voltage limited, current nominal). This burning in, according to the:
“ATTENTION / BEWARE” leaflet that accompanied them, distinguished two possible scenarios:
a). A procedure where just the fillament voltage is applied, non-stop, for 4 hours (!!!!!! ?????)
b). a procedure, which I used, involving a connected anode voltage, albeit a very low one, ranging from 50V to 250V (AC or DC) at the anode, via a series connected load that limits the current to no more than the specification limit for the lower range of operating voltages. In this scenario, it suffice to burn them for one hour. I noticed however, that a fully uniform color of the anode and beam former piece stabilized only but after some two hours of burning in.
Indeed, after the formatting process, the “silver” colored anode and cathode beam forming elements become grey-black. At the same time, a fair amount of vapor actually may be seen forming and then condensing at the lower parts of the glass of the tube.
So, one is already formatted, and this next one, just beginning the formatting process … Just freshly connected, so the arc is wild and jumping around all over the place. At the same time, the “cold” vapor of the yet unheated tube is clearly visible as a “morning mist” in the lower part of the glass:
Once the tubes are formatted, they may start their duties as mercury vapor rectifiers in some more serious application, with mid-range voltages of 2000V and 1 A of current. Actually, these tubes can also be operated up to 10 000 Volts, but then we need to cut down on the current to 0,5 A.
As with any mercury vapor tubes, the “ATTENTION” note also strongly advises to refrain from switching on the anode voltage any sooner than only after 30 seconds of full blown operation of the fillament heaters.
Some may say that a plain new silicon diode shall be a much better performer than these here, and much smaller …
But that glow of these mercury rectifier things … is to die for !!!