6BL7

Power Triode — Octal

RCA

Known Equivalents & Substitutes

6BL7GT6BL7GTACV5039

Similar Tubes (Not Drop-In Compatible)

6BX7GT

Similar pinout but different mu (10 vs 15) and ra (1300 vs 2150 ohms) — may not be a direct substitute in all circuits

Listed as substitute in Sams handbook but different characteristics — verify ratings before substituting

Electrical Specifications

Absolute Maximum

Anode Voltage (max)Max Plate Voltage500V

Anode Dissipation (max)Max Plate Dissipation (per section)10W

Cathode Current (max)Max Cathode Current (per section)60mA

Heater-to-Cathode Voltage (max)Max Heater-Cathode Voltage200V

Max Grid ResistorMax Grid Circuit Resistance

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

References