LED replaces T1.5 lamp

A station needed a simple switcher. In a storage room, I found a 3M Mincom 101 vertical interval switcher collecting dust. In the lab, it appeared to be fine inside and out, flat to 4.8 MHz. Maybe it was retired because half the selection indicator lamps had burned out, making it impractical to use. The lamps are T1 1/2 (Tubular, 1.5 x 1/8 inch diameter, or 4.8 mm). They're labelled S12V 30 mA, and appear to be available from Europe (R286 dashboard bulbs). But that would be very inconvenient.

I salvaged some white LEDs from broken cheap flashlights, chose a series resistor for about 6.5 mA current (your value depends on the voltage), and built a set of 10 replacements on pieces of Vero stripboard in an evening. Note that the stripboard should be trimmed to the edges of the copper traces to stay under 5 mm wide. And the leads go along the outer edges of the strips because the sockets are H-shaped. The new lamps are a bit brighter than the originals, so maybe I should have used more resistance, but I hope they'll last substantially longer than the 3000 hour spec on the old lamps. Another refinement would be to sand the LED ends to illuminate the buttons more diffusely.

Lamps, buttons.