To extend the life of bulbs, plug in the power supply circuit is a semiconductor diode that lowers the voltage across the lamp. But where to place it! If this causes you difficulties, install a diode in the base from the blown bulbs.
The diode type Д231, Д232, D245, Д246 cut conclusion with threaded and solder this side to the Central pad of the lamp cap. Then extra cap, drill a hole opposite the output diode. And that it does not touch the walls, lay within the base layer of paper or adhesive tape. Connect the soldering first, the output of the diode to the additional base, and then both of the cap.
E. DOLGOVESOV, Volgograd