6BL8

6BL8 is also designated ECF80. Completed sales put the typical price at $14.75 per tube.

Description

The 6BL8 is a triode-pentode in 9-pin miniature construction, designed for use as a frequency changer in television receivers. It has a coated unipotential cathode and may be used in any mounting position.

Ratings

The heater is rated at 6.3 volts and 0.45 ampere. The maximum plate voltage is 250 volts for both the triode and pentode sections. Maximum plate dissipation is 1.5 watts for the triode section and 1.7 watts for the pentode section. The maximum cathode current is 14 mA for both sections, and the maximum voltage between heater and cathode is 100 volts. The maximum grid #1 circuit resistance for the triode section is 0.5 megohm. For the pentode section, the maximum grid #4 circuit resistance is 1 megohm with automatic bias and 0.5 megohm with fixed bias.

For the pentode section, the maximum grid #2 voltage depends on cathode current: 175 volts at 14 mA cathode current, 200 volts at less than 10 mA cathode current, and 550 volts without current. The maximum grid #2 dissipation is 0.5 watt when plate dissipation exceeds 1.2 watts.

Capacitances

The triode section has an input capacitance of 2.5 pF and an output capacitance of 1.8 pF. The pentode section has an input capacitance of 5.5 pF and an output capacitance of 3.8 pF. The maximum plate-to-grid #1 capacitance of the pentode section is 0.025 pF. Inter-section capacitances are limited to 0.07 pF maximum between pentode plate and triode plate, 0.02 pF maximum between pentode plate and triode grid, and 0.16 pF maximum between pentode grid and triode plate.

Characteristics

At a plate voltage of 100 volts and grid #1 voltage of -2 volts, the triode section has a plate current of 14 mA, a transconductance of 5000 µmhos, and an amplification factor of 20. At a plate voltage of 170 volts and grid #1 voltage of -2 volts, the pentode section has a plate current of 10 mA, a grid #2 current of 2.8 mA, a transconductance of 6200 µmhos, a plate resistance of 0.4 megohm, and an amplification factor of grid #2 with respect to grid #1 of 47. The pentode section has an input resistance of 10,000 ohms at 50 MHz and an equivalent noise resistance of 1,500 ohms.

For mixer service with plate voltage 170 volts, grid #2 voltage 170 volts, grid #1 circuit resistance 0.1 megohm, and oscillator voltage 3.5 volts RMS, the triode section, with a cathode resistor of 330 ohms, shows a plate current of 6.5 mA and a conversion conductance of 2200 µmhos. Under the same plate, grid #2, grid #1 circuit, and oscillator conditions, the pentode section, with a cathode resistor of 820 ohms, shows a plate current of 5.2 mA and a conversion conductance of 2100 µmhos.

Alternative Designation

A French datasheet gives ECF 80 as an alternative designation for the 6BL8, with a heater rating of 6.3 volts at 430 mA, a 9C12 (noval) base, and an A22-2 envelope type. That sheet also lists a maximum grid #2 dissipation of 0.75 W for anode dissipation less than 1.2 W. Its pinout assigns pin 1 to the triode anode, pin 2 to triode grid #1, pin 3 to pentode grid #2, pins 4 and 5 to the filament, pin 6 to the pentode anode, pin 7 to the pentode cathode plus grid #3 and screen, pin 8 to the triode cathode, and pin 9 to the triode grid.

Equivalence is asserted only where the archive's own literature states it directly, in at least 40 separate documents. Tubes that merely substitute in some circuits are not listed here.

Per-tube prices from completed sales, 2026-02-05 to 2026-09-19. Matched pairs and quads are divided out. See the price index for how these move over time.

Original manufacturer datasheets for 6BL8, hosted by Frank Philipse's Electron Tube Data sheets.

Documents held here and used to write this page.

• RATINGS INTERPRETED ACCORDING TO DESIGN CENTER SYSTEM
• TRIODE PENTODE (filed under ECF80)