I get a lot of requests for vintage electric alarm clocks with lighted dials. Midcentury era lighted clocks used nightlight type screw-in bulbs that are relatively easy to replace. The mod 1960s-70s clocks, attractive and popular, are not so easy.
Clocks like the Seth Thomas "Cube Mini-Light" pictured use a tiny neon bulb with wire terminals that are wired into the power supply of the motor. The bulb filaments have about a 25,000 hour use life but after 40, 50 or 60 years they need replacement, depending on how much the clock was actually used. A flickering light is one indication that replacement is necessary, if the bulb still works at all.
Here is the original, burnt-out bulb on the right, with the replacement on the left., To work on 120v current, the bulb needs a 30k ohm resistor wired in.
One wire terminal and the wire on the resistor have been trimmed to fit, now the resistor needs to be soldered into place:
The bare terminal wires need insulating sleeves. I reused the original vinyl tubing for these. A piece of tape holds the tubing at the bulb base to protect against a short. The other ends are twisted in with the motor lead and power cord.
A quick, successful test shows a lit bulb with no shorting. The bulb goes into the fitting on the dial plate and is taped in place with electrical (or sometimes mylar) tape to hold it in and to direct the light to the dial.
The dials usually have layers of reflective and diffusive materials in an attempt to get an even ambient glow across the dial.
This one should light up the night for many years to come.