During the restoration of a Beocord 9000 cassette deck, the light bulb illuminating the peak program meter’s dB scale malfunctioned. This common issue stems from the age of the bulbs, as their leads tend to oxidize and break under pressure.

The initial state of the display, lacking illumination for the numbers on the dB scale, is shown below:

The bulb is inserted into a waveguide that distributes light across the scale, with a textured surface behind the numbers for diffusion. Images of the bulb’s position and its securing mechanism are provided:

The extracted bulb and its holder are depicted here:

To enhance longevity and resilience, the bulb was replaced with a custom LED-based solution. This approach, utilizing a PCB designed for a Beogram 4000 turntable’s tonearm indicator, ensures compatibility with the waveguide’s dimensions. Due to the separate red and green sections of the dB scale, a single amber LED wasn’t feasible.

The adapted PCB with a red/green LED is shown below:

A high-brightness red/green LED paired with specific resistors for each color ensures optimal brightness at the bulb’s 6.2V supply.

The LED in operation and its secure placement are depicted in the following images:

The waveguide illuminated by the LED and the final appearance with the bezel are presented below:

For comparison, the display of another Beocord 9000 with the original bulb is shown:

The LED-based solution achieves a comparable visual result with improved color accuracy, particularly for green hues, and more uniform illumination due to the LED’s focused light emission.