When looking at European MA/V mercury lamps, I’ve notified some have what appears to be some kind of filament wire wrapped around the arc tube. Does anyone know what purpose this serves? If there is even one.

Hello,

As much as I know it is used to stabilize the arctube and prevent bending of the inner assembly in transport.

best regards,

Alex

Does that also mean they can be ran horizontally instead of the usual vertical position required for medium pressure lamps?


Also, do most European MA/V require a cap up burning position similar to our North American ones?

To burn them horizontaly a special magnetic arc stabilizer is needed.

European catalogues generally state the lamps to be run base up.

As stated, most (but not all) medium pressure lamps are intended for base-up operation, but some were made in base-down configuration, for example the American made GE A-H1 lamp is base up, but the B-H1 is base down, those are rare beasts indeed, though, I know one member here has one, but don't recall who offhand. To run them horizontally, as Alex says, you need a magnetic arc deflector, these were built into the fixtures.

The wires around the arc tube on the Osram-GEC lamp are merely support wires to make sure the arc tube is central in the outer jacket.

Here is a small addition from the old paper with a drawing:


Source: H. Cotton, Electric Discharge Lamps, page 346, London 1946, Chapman & Hall Ltd.

Technically, the manufacturers have all realized it a little differently, but it was always for the stabilization of the arc tube in the outer bulb.
In the last years of production of these lamps, OSRAM and MELZ used stamped pieces of sheet metal instead of coiled wires.
CROMPTON fixed it without metal, just with two glass tubes bent open on one side and (presumably) small discs of asbestos as padding.

The British Mazda lamps also changed to stamped metal supports, Philips to a kind of metal strip support, and GEC to mica discs in the end.  This eliminated the need for the spiralled metal buffer springs.

Regarding burning position there was also an intermediate design which was optimised only for horizontal use without any magnetic deflector.  It was engineered with a slightly lower mercury vapour pressure, which meant that the arc did not become so constricted and therefore reduced convection currents in the arc tube and reduced the amount of upward bow.  By making the arc tube 2mm larger diameter the softening could be completely avoided.  That was sold in Britain as the type MA/H (horizontal) alongside the more common MA/V (vertical cap up) and the quite rare MA/D (vertical cap down).  Philips also made those in Holland but I am not sure if Osram Germany or the Americans produced those.  Due to the lower mercury pressure, their luminous efficacy was lower. 

Most of the later MA, HO and HgH lamps can in fact also be run horizontally because over time the aluminosilicate glass was improved to have slightly higher softening temperature.  Those were sold in Britain as the type MA/U (universal).

For more details about burning position, see http://www.lamptech.co.uk/Documents/M8C%20MA%20Lamp%20Developments.htm