Cathode Current (max)Max Cathode Current (per section)60mA
Heater-to-Cathode Voltage (max)Max Heater-Cathode Voltage200V
Notes
6BL7GT and 6BL7 are identical; the GT suffix denotes the glass-tubular envelope style.
6BL7GTA is a revised version with the same electrical characteristics but potentially tighter tolerances.
6BX7GT and 6DN7 are listed as substitutes in the Sams Tube Substitution Handbook but may not be exact equivalents in all circuits — verify ratings before substituting.
Tung-Sol datasheet (1950) rates mu=14, gm=7.0 mA/V, ra=2000 ohms; RCA (1953) rates mu=15, gm=6.2 mA/V, ra=2150 ohms. Both are within normal manufacturing spread.
No audio-specific load resistance or power output data in manufacturer datasheets — the tube was specified primarily for TV vertical deflection service.
Minimum cathode bias resistor per section is 220 ohms to protect against temporary failure of grid excitation.
Pin Layout — Octal
1Grid (triode 1)
2Anode (triode 1)
3Cathode (triode 1)
4
Socket-Compatible Tubes ⚠ Not electrically compatible