Neon Lamps
Neon lamps are used for at least two different things in Tek instruments:
- Indicator lamps, e.g., for power
- Voltage clamp, similar to how a zener diode is used
Neon lamps fail more than most other components. A common failure mode is for the leads to break off. Another failure mode is for the I-V characteristic to drift. Neon lamps are used as a voltage clamp in the CRT circuit for setting the CRT grid voltage in many Tek instruments. A typical example is seen in the 561A:
If the neon lamps fail, the CRT grid voltage will be affected. When in doubt, replace the neon lamps.