6BM8

6BM8 is also designated ECL82. Completed sales put the typical price at $21.50 per tube.

The 6BM8 is a combined triode-pentode with separate cathodes, intended for vertical deflection stages in television receivers and for preamplifier and output stages of tone amplifiers. It is an all-glass miniature tube with a nine-pin base, and the two systems are completely independent of each other. All electrodes are brought out to the base pins.

Construction

The 6BM8 has indirectly heated oxide-coated cathodes with parallel supply of AC or DC. The heater voltage is 6.3 V and the heater current is 0.78 A. The tube base is S 9/12 according to ČSN 35 8904. The TESLA datasheet states that the 6BM8 replaces the foreign type 6BM8, and gives the maximum weight of the tube as 20 g.

Ratings

For the pentode section, the maximum anode voltage when cold is 900 V, the maximum operating anode voltage is 600 V, the maximum positive peak anode voltage is 2500 V, and the maximum negative peak anode voltage is 500 V. The maximum anode dissipation is 5 W when the anode voltage is greater than 250 V, and 7 W when the anode voltage is less than 250 V. The maximum cold screen-grid voltage is 550 V, the maximum operating screen-grid voltage is 300 V, and the maximum screen-grid dissipation is 1.8 W, or 3.2 W with drive. The maximum cathode current is 50 mA. The maximum grid-circuit resistance is 1 MΩ with fixed bias and 2 MΩ with automatic bias. The maximum voltage between cathode and heater (DC or peak AC) is 100 V, and the maximum external resistance between cathode and heater is 20 kΩ.

For the triode section, the maximum cold anode voltage is 550 V, the maximum operating anode voltage is 300 V, and the maximum peak anode voltage is 600 V. The maximum anode dissipation is 1 W. The maximum cathode current is 15 mA, and the maximum peak cathode current is 250 mA. The maximum grid-circuit resistance is 1 MΩ with fixed bias, 3 MΩ with automatic bias, and 22 MΩ with grid-current bias. The maximum voltage between cathode and heater (DC or peak AC) is 100 V.

Applications

The datasheet recommends connecting pin 4, adjacent to grid 1 of the pentode, to the grounded end of the heater. It states that the triode section can be used without special precautions against microphony and hum with a single loudspeaker when the input voltage required for an output power of 50 mW of the output tube is greater than 10 mV. In this case, the AC voltage between heater pin 4 and the cathode should not exceed 5 V RMS, and the grid-circuit impedance at 50 c/s should not exceed 500 kΩ. With grid-current biasing, the maximum permissible value of the grid circuit resistance is 22 MΩ.

As a frame oscillator, the datasheet gives an optimum peak cathode current of 100 mA, and states that the circuit should be designed so that with a peak cathode current of 100 mA it still operates satisfactorily. It recommends limiting the amplitude of peak currents occurring with fresh tubes automatically to the maximum value of 100 mA. The circuit should be designed around a peak plate current not exceeding 85 mA at a plate voltage of 50 V and a grid #2 voltage of 170 V. At underheating (heater voltage 5.3 V), a peak anode current of 70 mA should be taken into consideration at a plate voltage of 50 V and a grid #2 voltage of 170 V, and a peak anode current of 80 mA should be taken into consideration at a plate voltage of 50 V and a grid #2 voltage of 190 V. The peak plate current of an average new tube is 135 mA at a plate voltage of 50 V, a grid #2 voltage of 170 V, and a grid #1 current of 0.3 µA. The maximum pulse duration is 4% of one cycle, with a maximum of 0.8 ms.

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, 2026-02-10 to 2026-09-15. Matched pairs and quads are divided out. See the price index for how these move over time.

Original manufacturer datasheets for 6BM8, hosted by Frank Philipse's Electron Tube Data sheets.

Documents held here and used to write this page.

• Kapacity mezi elektrodami: (filed under ECL82)
• 6BM8