Max Grid ResistorMax Grid Circuit Resistance0.25MΩ
Typical Operating
Anode Voltage (typical)Anode Voltage300V
Notes
Base is British 4-pin (B4), not the American UX4 — the two are physically different and not interchangeable without an adapter.
Early versions (pre-1933) were rated 12 W Pa max at 250 V / 48 mA. The later (post-war) version is rated 15 W at 300 V / 50 mA. All specifications here are for the final 15 W version per the Marconi July 1956 datasheet.
Datasheet-specified mu (5), gm (6 mA/V), and ra (830 Ω) are measured at Va = 100 V, Vg = 0 — an emission test point, not a practical operating condition. At the typical 250 V operating point, ra is higher (~1100 Ω) and mu is approximately 5.6.
Automatic bias is recommended. The total resistance in the grid circuit must not exceed 250 kΩ. A grid stopper resistor is required close to the valve holder to prevent parasitic oscillation.
In push-pull operation, separate bias resistors should be used for each valve. Separate filament windings are required for each PX4.
Also written as 'PX-4' or 'PX 4' in various sources.
Pin Layout — B4
1Anode
2Control Grid
3Filament
4Filament
Socket-Compatible Tubes ⚠ Not electrically compatible