Thorn Alpha 4

Lantern acquired in February 2004.

This lantern was all ready to be used, however its bowl and clips were required for another job, and so has not been installed anywhere. It has a fair amount of dust and dirt on it from being in the van, but this will wipe off easily. Alpha 4s are often used to replace failed Alpha 1s in Derby, but have also been used on new lighting schemes as well.

This photograph shows the Alpha 4 before I fitted the new bowl and clips. Yes, two clips are visible, but they are not yet glued in place. You heard me right; the clips have to be glued to the lantern!

A close-up of the gear reveals that the ballast is not a Thorn product, but a Transtar. I was surprised to see the capacitor fitted in the shoe, but the rest of the gear fitted in the lamp compartment. This lantern is narrower than the MA 90, and so there is not enough space to fit all of the gear components together! Looking again at the capacitor, notice that its incoming live (orange) wire is connected directly to the live terminal for the supply cable, rather than the NEMA socket. This would mean that, had the lantern entered service, the capacitor would have remained live, even if the rest of the lantern wasn't operational.

The label is located at the very front of the lantern and uses all kinds of coding, but the most important is the 'QA4' bit, as this is the Alpha 4 identification code. The number '2503' suggests that the lantern was produced on the 2nd May 2003.

Gluing the clips didn't take long, but the glue took a while to set. I put the bags below each clip 'area' in case of drips, but luckily there weren't any. The photocell socket has been wired out, but there is no cover over it.

When the glue dried, I fitted the bowl. Although all the clips are all the same, they have to be fitted differently to both sides of the bowl. One side opens completely, whereas the other acts as a hinge.


The lantern was fitted to an AC Ford AC872 wall bracket and powered up on Sunday, 28th August 2005.

Lantern warm-up video:


A cut-off bowl is also available for the Alpha 4, though it isn't as common as the regular semi-cutoff one.

Thorn Alpha 8 | Urbis ZX1


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