EL84 6BQ5 Mullard, used, Blackburn km1 code, test strong with at least 95%

Description

EL84/6BQ5 made by Mullard Blackburn

Price is for a single piece. We will select close values within our stock on orders of two ore more but there will most likely be no perfect match for a pair or quad.

These are km1 Mullard tubes from the early 1960ies. All have the km1 and additional Blackburn “B” coding. All are the same inside and out in terms of construction and do have the typical Mullard single round hole plate design.

These tubes show clear signs of use and stains in the glass (some more, some less) but test with a minimum of 95% in terms of mutual conductance and hence close to new regarding their performance. Call it burned-in.

Tested and guaranteed.

You do not find these often nowadays…. Very limited stock of these rare tubes available!

1. General Description

The EL84 is a power pentode vacuum tube developed by Philips in the 1950s. It was designed for audio output applications in both hi-fi systems and radio receivers. Its high gain, relatively low drive requirements, and compact 9-pin format made it extremely popular in both consumer and professional electronics.

• Type: Power Pentode

• Base: Noval (B9A, 9-pin miniature)

• Typical Output Power: ~5.7 W in single-ended Class A, up to 17 W in push-pull Class AB

• Structure: Beam-forming plates, suppressor grid internally connected to cathode

• Typical Load Impedance: 5–7 kΩ in single-ended mode

The EL84 offers high transconductance and sensitivity, requiring only modest drive voltage (~15 V peak) to reach full power output.

2. Audio Applications

The EL84 is one of the most iconic tubes in audio history, widely used in:

Hi-Fi Audio

• Found in classic integrated amplifiers and receivers (e.g., Leak Stereo 20, Dynaco SCA-35)

• Valued for its smooth, detailed, and harmonically rich sound

• Ideal for low-to-medium-power systems due to its clean Class A and AB performance

Guitar Amplifiers

• Used in classic designs like Vox AC15, Vox AC30, and Marshall 18W

• Delivers a bright, chimey, and responsive overdrive character

• Often praised for its musical distortion when pushed

Comparison to Other Tubes

• Versus the EL34, the EL84:

  • Has lower output power

  • Requires less drive voltage

  • Provides faster saturation and earlier breakup, ideal for expressive guitar tones

3. Industrial or Other Applications

While primarily designed for audio use, the EL84 also found use in:

• Radio and television audio output stages in consumer electronics

• Military and aerospace as a compact audio amplifier tube

• Test equipment, where small power output stages were needed

Due to its size and efficiency, it was used in portable and space-limited designs more frequently than larger output tubes.

4. Comparison to Similar Tubes

Note: The 6BQ5 is the American equivalent of the EL84 and is fully interchangeable.

5. Key Technical Data (Per Tube)

6. Construction and Special Features

• Envelope: Miniature glass, 9-pin Noval base

• Design: Beam-aligned pentode construction for improved efficiency and low distortion

• Suffixes:

  • EL84: Standard version

  • EL84/6BQ5: US equivalent

  • EL84M: Ruggedized version with higher ratings (military/industrial grade)

  • 6P14P-EV (Soviet): High-reliability version, long life (up to 5000 hrs)

• Other Features:

  • Compact size with high power output

  • Excellent for compact amplifier layouts

  • Well-suited for both single-ended and push-pull designs