I built this “tungsten roadwork beacon” as Clive calls it, using the parts given in my schematic (photo below).
I didn’t have a 6V, 90 mA lamp, so I simulated it by using three 20 ohm, 1/4 Watt resistors in series, which gives 60 ohms and 100 mA load with 6VDC. For an indicator I put a blue LED with its 1k series current limiting resistor across the 60 ohm load.
The “tungsten” incandescent lamp has very low resistance, about 1/10, when cold, so it draws ten times as much current when it is first turned on. So this lamp can draw as much as 1 amp when first turned on. The BC548 NPN transistor is a poor choice for the lamp driver because it can only handle 100 to 200 milliamps. Anything more exceeds its maximum ratings. So I used a PN2222A which can handle 800 mA.
Link to Big Clive’s YouTube video, with schematic https://youtu.be/tH2qW0tqhgo?si=QkHtGMSGMAhG5U27
