A tripler can refer to a voltage multiplier circuit made of diodes and capacitors that steps up an AC input voltage by a factor of three, commonly used in high-voltage power supplies. In RF engineering, a frequency tripler is a non-linear amplifier heavily biased to generate harmonics, where a tuned output filter selects the third harmonic of the input oscillator.
The CRT monitor's high voltage is dead, I suspect the high-voltage tripler block has shorted out internally.
Related terms
Voltage multiplier
An electrical circuit that converts a lower AC input voltage into a higher DC output voltage using a network of discrete components.
Frequency multiplier
A circuit that outputs a signal whose frequency is an exact integer multiple of its input frequency.
CRT
A cathode-ray tube is a vacuum envelope containing an electron gun and a phosphorescent screen.