Motorola 77XM AM/FM Radio found today

[jr_tech]

Originally Posted by davet753

Don't use anything except the bulb it was designed to use (or something close to it). On sets with series strung tube filaments, the bulb is a vital part of the circuit that, when blown or removed, will reduce the life of the tubes (especially the rectifier).

When you first turn on the radio the bulb glows brightly, quickly dims, and gets back brighter once the tubes are all warmed up. If you remove the bulb, the tube filaments get all that power at turn-on. A 50 cent bulb is a lot cheaper than a rectifier tube.

Usually very good advice for a series strung set. but in this case, the bulb is a 120 volt "night-light" sized bulb connected directly to the AC line after the line switch. Almost any candelabra base bulb (including a C-7 xmas bulb) may be substituted. The set does not use a rectifier tube, it has a Selenium rectifier.

jr