ECL113 TFK Triode/Pentode tube Rimlock Triode Powertube

ECL113 triode-output valve for compact one-tube amplifiers

The ECL113 combines an AF triode and a small output pentode in one compact Rimlock B8A envelope. The triode can provide voltage gain while the output section supplies current for a driver or loudspeaker-output stage.

This allows a compact single-ended amplifier, power-valve driver or transformer-coupled headphone output to be built around one valve per channel. Both sections share a common cathode, which must be considered when selecting the bias and feedback arrangement.

Suitable applications

• Compact one-valve and single-ended amplifiers
• Driver stages for larger audio output valves
• Transformer-coupled headphone and desktop amplifiers
• Stereo projects using optionally selected valves

Technical specifications

Valve construction

AF triode and output pentode with a common cathode

Offered production version

Telefunken or TFK

Base

Rimlock B8A, 8-pin

Heater

6.3 V at 0.6 A, indirectly heated

Triode reference condition

Va 250 V, Vg −1.5 V and Ia approximately 1.1 mA

Maximum triode plate dissipation

1 W

Output-pentode reference condition

Va 250 V, Vg2 250 V, Vg1 −3.5 V, Ia 25 mA and Ig2 3.5 mA

Output-pentode transconductance and resistance

Approximately 8.5 mA/V and 40 kΩ

Maximum output-pentode plate dissipation

6.5 W

Documented audio output

Approximately 2.25 W with a suitable output transformer

Dimensions

Approximately 21 mm in diameter and 70 mm body height excluding pins

Selection option

A matched/balanced option is available on the BTB product page

B8A connections – bottom view

Pins 1 and 8

Heater

Pin 2

Triode anode

Pin 3

Output-pentode anode

Pin 4

Output-pentode control grid g1

Pin 5

Output-pentode screen grid g2

Pin 6

Triode control grid

Pin 7

Common cathode for both sections and suppressor grid g3

Audio design notes

The shared cathode prevents completely independent cathode-bias settings for the two systems. In a new circuit, however, it may be incorporated deliberately into a local or overall feedback arrangement.

A correctly specified output transformer is required for a loudspeaker or low-impedance headphone. When used as a power-valve driver, the required voltage swing, input capacitance and possible grid current of the following valve must be checked.

Safety notice: Valve circuits may contain lethal anode voltages and should only be constructed and tested by suitably skilled users.

Questions about ECL113 audio applications

Is the ECL113 suitable for a complete one-valve amplifier?

Yes, the integrated triode can operate as the input stage while the output pentode drives a loudspeaker through a suitable transformer. The documented operating condition provides approximately 2.25 W of audio output from one valve per channel.

Can the ECL113 drive a larger audio output valve?

Yes, the triode provides voltage gain while the output pentode offers more current reserve than a typical high-resistance preamp triode. The voltage swing, anode load and input capacitance of the following output valve must be calculated for the project.

Can the ECL113 be used in a headphone or desktop amplifier?

Yes, it is suitable for compact audio amplifiers when used with an output transformer matched to the intended headphone or loudspeaker impedance. The shared cathode must be considered in the bias and feedback design.