6DC8

6DC8 is also designated EBF89. Completed sales put the typical price at $15.45 per tube.

Overview

The 6DC8 is a combined double diode and RF pentode vacuum tube, constructed as an all-glass miniature tube with nine contact pins on a base. It has indirect heating with an oxide cathode, and its heater can be powered in parallel or series from DC or AC.

Construction

Both diodes of the 6DC8 are completely independent of the pentode system except for the common cathode. The pentode is shielded by an internal shield connected to the cathode inside the bulb. All electrodes, including the suppressor grid, are brought out to base pins.

Ratings

The heater of the 6DC8 operates at 6.3 V with a current of 0.3 A. The maximum warm-up time is 30 seconds. The maximum plate voltage is 300 volts, with a maximum plate voltage without current of 550 volts. Maximum plate dissipation is 2.25 watts. The maximum screen grid voltage is 125 volts when plate current exceeds 8 mA, and 300 volts when plate current is less than 4 mA; maximum screen grid dissipation is 0.45 watt. Maximum cathode current is 16.5 mA. The maximum grid No.3 circuit resistance is 10,000 ohms, while the maximum grid No.1 circuit resistance is 3 megohms with automatic bias and 22 megohms with grid current biasing. Maximum voltage between cathode and heater is 100 volts, with a maximum circuit resistance between cathode and heater of 20,000 ohms. For the diodes, maximum peak inverse plate voltage is 200 volts, maximum DC diode current is 0.8 mA, and maximum peak diode current is 5 mA. The maximum plate current is 0.8 mA, with a maximum peak plate current of 5 mA. The amplification factor of grid No.2 with respect to grid No.1 is 20.

Capacitances

The input capacitance is 5 pF and the output capacitance is 5.5 pF. Grid-to-anode capacitance is less than 0.004 pF, and capacitance between grid No.1 and the heater is 0.05 pF. Each diode has a capacitance of 2.5 pF with respect to the cathode. Diode I has a capacitance of 0.15 pF with respect to the anode, and diode II has a capacitance of 0.025 pF with respect to the anode. Capacitance of diode I with respect to grid No.1 is less than 0.0008 pF, and of diode II with respect to grid No.1 is less than 0.001 pF. Capacitance of diode I with respect to the heater is 0.015 pF, and of diode II with respect to the heater is 0.003 pF.

Applications

The 6DC8 is suitable for RF, IF, and AF amplifiers. The double diode serves as an amplitude demodulator and a source of AVC voltage. The Czech datasheet, published by Ministerstvo přesného strojírenství, describes the TESLA EBF89 as a replacement for the 6DC8.

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, 2026-07-02 to 2026-09-22. Matched pairs and quads are divided out. See the price index for how these move over time.

Original manufacturer datasheets for 6DC8, hosted by Frank Philipse's Electron Tube Data sheets.

Documents held here and used to write this page.

• MINISTERSTVO PŘESNÉHO STROJÍRENSTVÍ (filed under EBF89)
• 6DC8

1 further designation appears alongside 6DC8 in the literature but below the evidence threshold used here, so it is not listed as equivalent.