Loctal triode with same pinout but 14V heater — not interchangeable without heater rewiring
6J5GT
Electrically identical but uses Octal base — not a drop-in replacement
7B4
Same loctal pinout but high-mu triode (μ≈70) — very different electrical characteristics
Electrical Specifications
Absolute Maximum
Anode Voltage (max)Max Plate Voltage300V
Anode Dissipation (max)Max Plate Dissipation2.5W
Cathode Current (max)Max Cathode Current20mA
Heater-to-Cathode Voltage (max)Max Heater-Cathode Voltage90V
Typical Operating
Notes
The 7A4 is the loctal equivalent of the octal 6J5 and represents one section of the 7N7 twin triode, just as the 6J5 is one section of the 6SN7.
Nominal heater voltage is 7.0V for household receivers (117V line); for a-c service the 7-volt rating corresponds to a 130-volt line condition. Typical operating heater voltage is 6.3V. Also suitable for automotive receiver service at 6.6V battery terminal voltage.
The XXL (Philco designation) is regarded as electrically interchangeable, though it exhibits slightly higher plate resistance and variation of amplification factor across operating points.
Loctal base pins are prone to corrosion over time — clean contacts may be needed for reliable operation of NOS tubes.
Pin Layout — Loctal
1Heater
2Plate
3No Connection
4
Socket-Compatible Tubes ⚠ Not electrically compatible