Question: cage filament supports

[PCris]

Hello all,

Perhaps one or more of you could "enlighten" me (pun intended!) on a question I have concerning filament supports in Mazda cage filament lamps. I've noticed infrequently that some have heavier copper supports. Is this an indicator of an earlier lamp, or does it have more to do with some specialized purpose?

Any information, facts or opinions anyone could share with me about this will be greatly appreciated. Thanks!

PCris

[James]

The first lamps used copper support wires.  Since copper is a very soft metal, it was necessary to use wires of rather large diameter.  Thick wires were also necessary because if too thin, they would heat up too much and further soften, losing their supporting characteristics.

Using thinner wires is desirable both on the grounds of cost, as well as the fact that thinner wires conduct less heat away from the filament and result in higher lamp efficacy.  To be able to reduce the wire diameter, a strong metal is required, which can also withstand the high operating temperature of the filament.  Tungsten would be suitable but it's a very expensive metal, which could be justified only for the filament itself.

The advent of thinner support wires had to wait for the development of wires made from the metal Molybdenum.  Molybdenum is an extremely strong metal of high melting temperature, rather similar to tungsten but considerably cheaper.  Moly is still used today in filament support wires.  The changeover from copper to moly support wires occured from about 1915 onwards.

[PCris]

James,

Many thanks for your most helpful and informative response to my question regarding cage filament supports. Before posting this question, I had searched Howell & Schroeder, but even though there is a wealth of detail on development of bulb manufacturing techniques, I could find nothing on this admittedly somewhat obscure aspect of early tungsten bulbs.

Shortly after I posted this question, I saw a Mazda on e-bay with the thick copper supports and bid on it. After it arrived, I observed other features in addition to the copper supports that seemed to indicate an early manufacture - the welded lead-ins going through the stem press, and the attachment of the filament to the leads using the earlier crimped tubes as opposed to the simplified "hook" connection. From this, I deduced that probably the copper supports are a sign of earlier lamps. So it was nice to have your confirmation of this as well as the other details which I am pleased to learn about. Again, thanks for answering.

PCris