12.6V heater version of 7F7 with same Loctal base and pinout — requires different heater supply
6SL7GT
Electrically identical but uses Octal base — not pin-compatible with Loctal socket
Electrical Specifications
Absolute Maximum
Anode Voltage (max)Maximum Plate Voltage300V
Anode Dissipation (max)Maximum Plate Dissipation per Plate1W
Heater-to-Cathode Voltage (max)Maximum Heater-Cathode Voltage90V
Typical Operating
Anode Voltage (typical)Plate Voltage250V
Notes
Sylvania originally rated the heater at 7.0V nominal to accommodate lead-acid battery charging voltage in mobile equipment; Tung-Sol and later datasheets standardize at 6.3V. The heater is robust across this range.
Only Sylvania, Raytheon, and National Union manufactured Loktal tubes; other branded versions were typically rebranded Sylvania production.
Loktal pins are susceptible to corrosion — clean contacts are essential for reliable operation.
All elements except the common heater are brought out separately, allowing each triode section to operate independently.
The Sams Tube Substitution Handbook lists no drop-in substitutes for the 7F7, reflecting the limited adoption of the Loctal base format.
Pin Layout — Loctal
1Heater
2Cathode 1
3Anode 1
4
Socket-Compatible Tubes ⚠ Not electrically compatible