Electrically similar but max reservoir capacitor is 60 µF vs 4 µF — different filter design constraints
Electrical Specifications
Absolute Maximum
Anode Voltage (max)AC Voltage per Plate (max RMS)500V
Rectifier
Peak Inverse VoltagePeak Inverse Voltage (capacitor input)1,600V
Voltage Drop (typical)Voltage Drop (approx. at 350 mA, choke input)30V
Max C-input Filter CapacitorMax C-input Filter Capacitor4µF
Notes
Maximum reservoir capacitor is only 4 µF (capacitor-input filter), much lower than the GZ34's 60 µF. This is a critical design constraint — most modern amplifier designs using large reservoir caps cannot use the GZ37 without modification.
Minimum series resistance per anode (Rftm) of 75 Ω is required for capacitor-input filter operation to limit peak charging current.
Choke-input filter operation allows significantly higher output current (350 mA vs 250 mA) and higher PIV rating (1850 V vs 1600 V).
Pin-compatible with 5U4G/5U4GB but the 5U4G is directly heated while the GZ37 is indirectly heated, giving the GZ37 a slower warm-up and reduced inrush stress on filter capacitors.
The CV378 made by GEC is designated U54 or 53KU; the Mullard-manufactured version is designated GZ37. Both meet the same CV378 military specification.
Pins 3, 5, and 7 are physically absent on the octal base (NP), not merely unconnected.
Pin Layout — Octal
1No Connection
2Heater
4Anode 2
6Anode 1
8
Socket-Compatible Tubes ⚠ Not electrically compatible