Amplifier 3 Watt Standard

Mullard Wireless, London (see also Mullard Radio Valve)

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  • Year
  • 1956–1962 ?
  • Category
  • Kit (Parts plus instruction) or building instructions only
  • Radiomuseum.org ID
  • 367738

Click on the schematic thumbnail to request the schematic as a free document.

 Technical Specifications

  • Number of Tubes
  • 3
  • Main principle
  • Audio-Amplification
  • Wave bands
  • - without
  • Power type and voltage
  • Alternating Current supply (AC) / 50 Hz, 200 /220/ 240 Volt
  • Loudspeaker
  • - This model requires external speaker(s).
  • Power out
  • 3 W (max.)
  • Material
  • Metal case
  • from Radiomuseum.org
  • Model: Amplifier 3 Watt [Standard] - Mullard Wireless, London see
  • Shape
  • Chassis only or for «building in»
  • Notes

  • The Mullard Three‑Watt Amplifier is a small single‑ended audio amplifier design using one EF86 voltage‑amplifier pentode, one EL84 output pentode, and an EZ80 full‑wave rectifier. It was first published in Radio Constructor, April 1956, and later included in Mullard – Circuits for Audio Amplifiers (1959). Mullard intended the design as a simple, mains‑operated, high‑quality amplifier for crystal and ceramic pick‑ups and for compact domestic hi‑fi systems. It became widely adopted by hobbyists, kit suppliers, and small manufacturers during the late 1950s and early 1960s.

    Circuit concept and performance
    The amplifier delivers approximately 3 W output with an overall sensitivity of 100 mV, allowing direct connection of crystal and ceramic pick‑ups or passive equaliser networks. The EF86 is operated at low current and reduced electrode voltages to permit direct coupling to the EL84 grid. This arrangement provides high gain with minimal loading and allows about 20 dB of overall negative feedback while maintaining stability.

    Negative AC feedback is applied from the secondary of the output transformer to the EF86 cathode. Mullard also provided an optional bass‑boost arrangement by reducing low‑frequency feedback. Frequency response is essentially flat from 35 Hz to 30 kHz, with up to 20 dB treble cut and 15 dB bass boost available. Total harmonic distortion rises rapidly above about 3.5 W, marking the onset of overload. Output impedance is under 1.5 Ω when matched to a 15 Ω loudspeaker, giving a damping factor greater than 10.

    Controls

    • RV1 – Volume
    • RV2 – Treble
    • RV11 – Bass

    These controls form part of the feedback and tone‑control network described in the Mullard publication.

    Power supply
    The power supply uses an EZ80 rectifier fed from a 300‑0‑300 V, 60 mA mains transformer. Reservoir and smoothing are provided by a 50 + 50 µF electrolytic capacitor. A supply tap (C9 in the Mullard diagrams) is provided for powering a companion pre‑amplifier.

    Construction and commercial use
    This amplifier was a published design only; Mullard did not manufacture it as a finished product. It was intended for home construction and for use by commercial kit suppliers. Mullard recommended several suitable commercial output transformers, including types by Colne, Elden, Elstone, Gardners, Gilson, Hinchley, Parmeko, Partridge and Wynall. Numerous UK and Commonwealth kit builders adopted the design, often following the Mullard layout closely.

    See also the  Control‑less version intended for use with an external pre‑amplifier or stereophonic equipment.

  • Mentioned in
  • -- Original prospect or advert (Radio Constructor April 1956, p. 564-569, 579)
  • Literature/Schematics (1)
  • - - Manufacturers Literature (Mullard – Circuits for Audio Amplifiers, 2nd Edition, 1959. P.53-60)
  Mullard – Circuits for Audio Amplifiers, 2nd Edition, 1959. P.53-60 3744 KB
  • Documents regarding this model
  • Author
  • Model page created by Gary Cowans. See "Data change" for further contributors.

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