In article ,
Madness wrote:

Just acquired a bunch of these lamps. They're in the same mini-bayonet
style as lamps like the #44/47. But would anyone know if these lamps can
be connected directly to 120 volts? Or do they need a resistor, @ if so,
what value?

Madness-

NE-51 does NOT have a resistor inside!

One thing you can do with them, is build a relaxation oscillator. From
a 90 to 100 volt DC source, connect a series resistor, with a capacitor
across the bulb. Perhaps 470K Ohms and 1 uF. Try different values to
change the flashing rate. For smaller values, it can be used as an
audio oscillator.

Another variation is to have several bulbs, each with its series
resistor. But the capacitors are connected from bulb to bulb in a ring.
The result is a somewhat random flashing. I once built one with 5
generic neon lamps using two small 45 Volt batteries in series. Some
people would become engrossed, trying to figure out the flashing
sequence!

Fred