From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Tests carried out on 3.5-volt lamps for instrument-group lighting following frequent failures.
| Identifier | ExFiles\Box 167\1\ img262 | |
| Date | 10th June 1938 | |
| 6116 To By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/RC.{R. Childs} c. to By/RD. c. to Rm{William Robotham - Chief Engineer}/FD.{Frank Dodd - Bodies} Rm{William Robotham - Chief Engineer}/RC.{R. Childs}7/JH.10.6.38. INSTRUMENT-GROUP LIGHTING WITH 3.5 VOLT LAMPS. The type of lamp used for lighting the instruments in R.R. scheme 1110, is the Osram 3.5 volt, .3 ampere lamp. As a result of the reported frequent failure through burning out of these lamps, on car 26.G.VI in France, a series of tests have been carried out. These were for the purpose of ascertaining the length of life of this type of lamp, when running under various conditions of supply voltage. The series arrangement of lamps is generally unsatisfactory, unless the lamps are accurately made as regards filament resistance, and are capable of giving good service when run above normal voltage. This is because any lamp in a series which has a resistance below normal, causes an extra load to be thrown on to the normal lamps, thereby reducing their burning hours. A test in this connection was made with a set of standard lamps. These were arranged in two parallel groups each of three lamps in series as on the car, with the difference that one group C, was continuously switched on, while the other group A, was switched alternately on and off. With a voltage of 10.5 volts (3.5 volts per lamp) applied to the combination, the volts across individual lamps were as follows Group C. 1 2 3 With group A switched on 3.43 v.{VIENNA} 3.37 v 3.65 v.{VIENNA} off 3.52 v.{VIENNA} 3.41 v.{VIENNA} 3.72 v.{VIENNA} | ||