Tesla SHC with Monolithic Seal 2-Piece PCA

Tesla's engineers have shown immense creativity through their experimentation and efforts to improve the HPS lamp. This example is attributed to the engineer Ludvik Sokol who was responsible for many of the creations.

It is one of the earliest known HPS lamps fabricated from just 2 pieces of PCA ceramic. Generally a minimum of 3 pieces are required, consisting of the central body portion, and then a plug to reduce the diameter of the ends such that a niobium feedthrough can be sealed in place.

In this lamp, the PCA tube has been pressed with one end already partially closed (this is the end on the right hand side in the main photo). It is then possible to seal the niobium feedthrough directly into the main body of the PCA tube, without the need for any additional components. The electrode is first welded to an Nb wire and the back space set by crimping. The assembly is then dropped into the open end of the tube, such that the Nb wire only falls through the small opening at the monolithic end. Another crimp is then made on the protruding section of Nb wire to fix it in place, and it is frit-sealed into the PCA.

Following dosing of the sodium amalgam, the second end is then sealed according to the standard Tesla fashion. The back space is set with a small Nb crosswire (see second thumbnail photo). It is frit sealed into the open end of the tube, with a small ring of PCA serving to accomodate the difference in diameter between the opening of the arc tube, and that of the Nb feedthrough. The second end, of course, has to have an opening large enough for the electrodes to be fed into the arc tube.
Manufacturer: Tesla Holesovice
Lamp Power: 70 Watts
Lamp Current: 0.98 Amps
Lamp Voltage: 90 Volts
Cap Type: E27s/27 Ni plated brass + porcelain
Bulb Finish: Clear Soda-lime glass
Bulb Type: ED-75 ED-23½ in eighths/inch
Overall Length: 160 mm 6¼ inches
Light Centre Length: 86 mm 3 3/8 inches
Arc Length:
Electrodes: Backwound Tungsten Barium Calcium Tungstate
Atmosphere: Na,Hg | Xe Outer: Hard Vacuum
Luminous Flux: 6,000 lm @ 100 hours
Luminous Efficacy: 85.7 lm/W @ 100 hours
Colour Temperature & CRI: CCT: 1900K CRI: Ra 25
Chromaticity Co-ordinates: CCx: 0.542 CCy: 0.415
Burning Position: Universal
Rated Lifetime: 12,000 hours to 50% survival
Warm-up & Re-strike Time: 5 minutes 5 minutes
Factory: Praha Factory No.1 Czechoslovakia
Date of Manufacture: 1987
Original & Present Value: Unknown
References: 1) Private communication - Stanislav Slabyhoudek.