Replacing a HAM IV rotator display bulb by LEDs
My 1981 vintage rotator control box blew its display backlight. Instead of searching for a suitable replacement bulb, I decided to replace it with a LED strip.
The replacement is quite simple. The original LED bulb is preserved for historical purposes but slid aside to make room for mounting a piece of LED strip on top of the display. The voltage from the lamp (2 5V AC) is rectified using a small power diode, in my case an 1N4004, sent through a current limiting resistor, and send through the LED strip. A 10microF across the rectified supply is used to smooth the voltage and thus avoid flickering.
The LED strip is hot-glue mounted to the top of the display, with the LEDs pointing downwards into the display face. Perhaps a longer LED strip which covers the width of the display would be better.
The result is a well-lit display. Perhaps a piece of diffusing plexi could be added to better spread the light.
Here’s a circuit diagram in true DaveCAD-style.