Key points:

• No heater: it operates cold; no warm-up like normal vacuum tubes.
• Extremely stable voltage: once struck, it maintains a consistent ~85V across its terminals.
• Sometimes found in high-end vintage test equipment, oscilloscope circuits, and audiophile-grade tube gear (rarely, but occasionally).
• The 85A2 is equivalent to other reference tubes like the 0A2, but with different operating voltages (0A2 is 150V, 85A2 is 85V).

• Type: Voltage reference tube (cold cathode)
• Application: Voltage regulation, precision circuits
• Striking Voltage (approx.): 85V
• Maintaining Voltage: 85V ± tolerance (very stable)
• Current Range: Typically 1 to 10mA
• Base: B7G (7-pin miniature)
• Heater: None (cold cathode tube — no heater required)
• Gas Filling: Neon (often with small additives for performance)