Atlas Alpha 3
Lantern acquired in November 2019.
This lantern is one of six that were removed, with permission, from the former Tecnograv (more recently, AF Reprographics) site on Nottingham Road, Spondon on Tuesday, 26th November 2019, prior to the site's redevelopment. These Alpha 3s are notable in that they are the rarer, original type with a (supposedly) hermetically sealed optical unit, where the entire canopy and bowl slid forwards from the rest of the lantern, in order to allow for lamp changes to take place - more photographs of the installation, as it existed in 2015, can be viewed here. With sincere thanks to fellow collector John Thompson for organising the rescue of these lanterns, and to Platinum Electrical for undertaking the removal. The Alpha 3, as a design, dates from 1957, having been introduced at the Association of Public Lighting Engineers' (APLE) conference in that year for use with the then-new Atlas Fluorescent Mercury lamps (MBF/U). The lantern is also noteworthy in that it was the preferred choice for lighting the service areas of the newly-opened M1 Motorway in 1959.
The column to the left in the picture below is believed to be the one that supported the Alpha 3 that entered the Collection. This is how the scene appeared in July 2015.
The sealing gasket that should have ensured that the lamp area was watertight had, clearly, failed on this example.
All of the Stanton 8F concrete columns were heavily spalled around the column / bracket joint, increasing the chances of the brackets giving way under their own weight and falling to the ground, and the lanterns being ruined in the impact.
Whilst I had thought that the bowl had let in water and nothing else, the 'substance' visible within the water turned out to be some sort of partially-melted plastic bag - how the Dickens did that end up there, and why?!
The most noticeable difference between this version of the Alpha 3 and later types is the absence of any bowl retaining clips pressed against the side of the canopy exterior. Instead, two larger toggles attached to the rear section of the lantern hold the canopy in place in normal circumstances. Interestingly, a similar setup existed with later versions of the fabulous Alpha 1 low pressure sodium lamp lantern (which was launched in 1955, and provides the basis of the Alpha 3's design), but not with the original Atlas version. A short stub of the old bracket tube remains attached to the rear section - the three 3⁄8″ grub screws securing the two parts are likely to be seized, and if this is the case, will have to be drilled out and replaced, assuming that they will not loosen with some heat treatment.
The canopy itself is the least-changed component in this Alpha 3 in comparison to later versions; the same ridged aluminium pressing is employed here; however, twelve brass nuts and bolts spaced around the canopy's circumference hold the bowl in place. Incidentally, the lantern measures (approximately - these dimensions are taken from the later version) 291⁄4″ (743 mm) × 181⁄4″ (464 mm) × 12″ (300 mm).
The bowl is Perspex, and has become slightly translucent in its lifetime, owing to UV degradation produced by a combination of the lamp and sun. Notice the moss that has grown around the bowl rim - the lantern has created life! Within the optic, an aluminium tube is visible above the lamp - this is what the canopy slides along when a lamp change is required. There are no manufacturer's details presented anywhere on this lantern - the reason being that the same lantern was marketed as (both) the Atlas Alpha 3 and AEI Optispec One simultaneously for a time. With the AEI name disappearing in 1967, following its buyout by GEC, all of the AEI lantern names disappeared; the products becoming solely Atlas (and later, Thorn) branded after the takeover, owing to GEC having its own street lighting range.
The two locking toggles are brass, as is apparent by the verdigris oxidisation that has formed on the exposed metalwork. The rear section is shaped in such a way that the clips tuck into it when engaged.
With the toggles disengaged, the canopy is free to slide along the tube. The canopy needn't be slid the full length of the tube, as the lamp is soon clear of the optic, but the extra distance provides a little additional space for engineers to work on the lantern. The 'greenhouse'-like odour that emanated from the optic when the two pieces were separated initially was somewhat overpowering, but a lot more pleasant than I was expecting!
A separate plate bolted to the back of the canopy reduces the optic's opening to one that is only slightly wider than the diameter of a 400 W elliptical lamp; the maximum permitted wattage that this lantern could accommodate.
A slotted cheese-head bolt located towards the end of the tube ensures that the canopy cannot be removed completely.
Despite the inside of the canopy serving as a means of reflection in its own right, additional corrugated reflector panels are riveted to the metalwork.
Looking the other way, through the bowl.
With the camera positioned within the optic, and the self-timer activated, this (rather unusual) view is captured.
The Wotan-made 250 W mercury lamp carries the date code 'qh3', which signifies that it was made in Spandau, Berlin, in March 1987. Lamps carrying the same date code were fitted in the other five lanterns - they cannot have seen much use to have lasted 32 years, but then again, all are in the same sort of condition as this example is - the arc tube is completely blackened, and a portion of the phosphor coating has burnt off from the lamp's outer bulb. A factor in this is that the lamps will have been over-run quite substantially; 400 W ballasts were fitted in the column bases!
The lampholder is attached to a plate that provides a plug to the optic area. Rather than its wires passing through a rubber grommet or similar, the wires connect to two bolts that are separated by a strip of insulating material, and pass through the plate. I assume that two further wires are attached on the other side of the bolts, but as the grub screws that hold the plate in place are corroded beyond reuse, as yet, I am unsure as to how the supply cable terminates into the lantern. The insulating material shows signs of burning; probably, as a result of the trapped water in the lantern creating a short between both terminals.
Five of the gear sets are pictured below; four remained attached to their original backboards, whilst the fifth ballast was in very poor condition, having lost much of its casing, and one of its fixing brackets, to corrosion. The fourth ballast is slightly wider than the others are, and may be a later replacement, although the wiring remains the same. Curiously, the backboards show no signs of a cut-out, or any form of supply cable termination, having been attached.
One of the ballasts retained a very faint stamp mark - this confirmed that the 250 W lamps would have been over-run in service, and the Atlas logo suggests that these lanterns were, indeed, Alpha 3s, as opposed to Optispec Ones.
The BICC C2125 capacitors are dated to June 1962. The 15 µF rating of the capacitor is surprising; for 400 W MBF lamps, a capacitor with a value of 20 - 25 µF is recommended, but 15 - 20 µF capacitors are acceptable with 250 W lamps...had the lanterns always been intended as 250 W, and if so, why did no-one notice that the ballasts were not correct? Very strange all round...
The rather sorry-looking fifth ballast is unlikely to be of any electrical use any longer, but would make a fine doorstop!
Thorn Beta 5 (1970) | Philips MA 90
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