Monoblock MA15 Mk 1

Radford Electronics Ltd.; Bristol

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  • Year
  • 1960 ?
  • Category
  • Audio Amplifier or -mixer
  • Radiomuseum.org ID
  • 360483

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

 Technical Specifications

  • Number of Tubes
  • 5
  • Main principle
  • Audio-Amplification
  • Wave bands
  • - without
  • Power type and voltage
  • Alternating Current supply (AC) / 50 Hz, 200/240 Volt
  • Loudspeaker
  • - This model requires external speaker(s).
  • Power out
  • 15 W (undistorted)
  • Material
  • Metal case, TUBES VISIBLE
  • from Radiomuseum.org
  • Model: Monoblock MA15 Mk 1 - Radford Electronics Ltd.;
  • Shape
  • Tablemodel, Box - most often with Lid (NOT slant panel).
  • Dimensions (WHD)
  • 8.5 x 6.25 x 17 inch / 216 x 159 x 432 mm
  • Notes

  • The Radford MA15 series of amplifiers was a well-regarded line of vacuum tube audio amplifiers produced in the 1960s.

    There were four versions:

    1. MA15 Mk1: This was the original version of the amplifier.
    2. MA15 Mk2 Early: An updated version of the original design.
    3. MA15 Mk2 Late: A further refinement of the Mk2 design.
    4. CMA15: This was a kit version of the MA15 amplifier.

    The original Radford MA15 Mk1 was a monoblock valve power amplifier with the following characteristics:

    • Output power: 15 watts
    • Circuit design: Based on a variant of the classic Philips/Mullard '5-20' circuit
    • Output stage: Push-pull EL34 pentodes in ultra-linear configuration
    • Phase inverter: Triode-triode configuration
    • Feedback: Lower amount compared to Mk2
    • Output transformer: Less advanced than Mk2, with first resonance around 60-70kHz
    • Performance: Higher distortion levels, especially at frequency extremes
    • Power delivery: Limited ability to deliver full power at high frequencies

    Radford MA15 Mk1 Output Transformer

    • Resonance Frequency: The Mk1 output transformer had a first resonance around 60-70kHz.
    • Performance: This design resulted in higher phase shifts and distortion at high frequencies, limiting its ability to deliver full power at the upper end of the audible spectrum.
    • Design Complexity: The transformer was less advanced, which contributed to reduced stability and slightly inferior sound quality compared to the Mk2.
  • Price in first year of sale
  • 23.00 GNS
  • Author
  • Model page created by Gary Cowans. See "Data change" for further contributors.

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