Elwell Amplifying Unit

Elwell, C. F., Ltd.; London

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  • Year
  • 1922/1923
  • Category
  • Radio module pre 1926 (not a part, not a key)
  • Radiomuseum.org ID
  • 363586

 Technical Specifications

  • Number of Tubes
  • 1
  • Main principle
  • Audio-Amplification; 1 AF stage(s)
  • Wave bands
  • - without
  • Power type and voltage
  • Storage and/or dry batteries
  • Loudspeaker
  • - For headphones or amp.
  • Material
  • Wooden case, TUBES VISIBLE.
  • from Radiomuseum.org
  • Model: Elwell Amplifying Unit - Elwell, C. F., Ltd.; London
  • Shape
  • Tablemodel, Box - most often with Lid (NOT slant panel).
  • Dimensions (WHD)
  • 3.5 x 2.3125 x 2 inch / 89 x 59 x 51 mm
  • Notes

  • The Elwell Amplifying Units, introduced in 1922, were modular valve amplification components that combined a valve holder with a fully enclosed intervalve transformer in a single patented assembly. Designed for convenience and reliability, each unit provided one complete stage of amplification without requiring soldering or external transformer wiring.

    Design and Construction

    • The unit consisted of an ironclad intervalve transformer and valve socket mounted together, with all permanent connections pre-made and embedded in insulating compound.
    • Grid connections were given extra-long leakage paths and full insulation to reduce unwanted "howling" and noise, a common problem in amateur receivers of the period.
    • The transformer was encased in iron, allowing several units to be mounted close together without acoustic feedback effects.
    • Provided with tapped fixing holes on two sides and the base, the units could be panel-mounted, shelf-mounted, or left freestanding.

    Function and Variants

    • The primary version, marketed as a "note magnifier," offered straightforward audio-frequency (AF) stage amplification.
    • Alternate variants included an oscillation amplifier and a rectifying unit, enabling different circuit functions using the same modular construction.
    • Multiple amplifying units could be linked, with two or more stages coupled together for greater signal gain.

    Electrical and Practical Features

    • Operation required only inserting a valve and connecting external leads to the clearly marked screw terminals.
    • No soldering was necessary, making them especially suitable for amateur constructors and small-scale manufacturers.
    • Self-contained permanent connections and compound embedding ensured long-term reliability.
    • The valve holder incorporated an earth clip for secure grounding and silent operation.
    • Price (1922): 39 shillings 6 pence (excluding valve).
  • Price in first year of sale
  • 1.98 GB £
  • Author
  • Model page created by Gary Cowans. See "Data change" for further contributors.

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