The plasma tubes generally ionise at 80 kHz but we allow a margin for tube manufacturing variables and different operating ambient temperatures. Spooky Central will actually work down to 0Hz but the tube ionisation is so brief that it cannot be detected. The maximum frequency is about 3.6 MHz, but again this depends on many factors like the length, spacing and orientation of the white wires feeding the tube, tube type and more. Adding a high speed gate (about 20 Hz) increases the operation range. We have run a Spooky Central at 8 MHz using a short wire and 20 Hz gating.
Source: Spooky Central Q&A