Electrically similar but max reservoir capacitor is only 4 µF vs 60 µF — not interchangeable in most circuits
Electrical Specifications
Absolute Maximum
Anode Voltage (max)AC Voltage per Anode (max RMS)500V
Rectifier
Peak Inverse VoltagePeak Inverse Voltage1,400V
Voltage Drop (typical)Voltage Drop (approx. at 300 mA, choke input)28V
Max C-input Filter CapacitorMax C-input Filter Capacitor60µF
Notes
Indirectly heated (unipotential cathode) — cathode is internally tied to one side of the heater (pin 8 = h,k) because heater-cathode insulation is insufficient to withstand the full operating voltage.
Higher current rating than the GZ32 and GZ34 (both 125 mA C-input). The GZ33 delivers 250 mA with capacitor-input filter or 300 mA with choke-input filter.
Capacitor-input filter requires minimum series resistance (Rlim) per anode that increases with applied voltage: 140 ohm at 2x300V, 200 ohm at 2x400V, 250 ohm at 2x500V.
Shares base pin layout with GZ32 and GZ34 — same octal pinout. Not a drop-in replacement due to significantly higher heater current (3.0 A vs 1.9 A for GZ34) and different voltage drop characteristics.
The GZ37 is electrically similar but rated for a much lower maximum reservoir capacitance (16 µF vs 60 µF for the GZ33).
Pin Layout — Octal
1No Connection
2Heater
3No Connection
4
Socket-Compatible Tubes ⚠ Not electrically compatible