Mudlark A205, 20-watt per channel, Class A2 triode amplifier

Silicon Chip Publications Pty. Ltd; Brookvale NSW

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  • Year
  • 2005
  • Category
  • Audio Amplifier or -mixer
  • Radiomuseum.org ID
  • 324357

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

 Technical Specifications

  • Number of Tubes
  • 6
  • Number of Transistors
  • Semiconductors present.
  • Semiconductors
  • Main principle
  • Audio-Amplification; Hi-Fi-High End products
  • Wave bands
  • - without
  • Power type and voltage
  • Alternating Current supply (AC) / 240 Volt
  • Loudspeaker
  • - This model requires external speaker(s).
  • Material
  • Metal case, TUBES VISIBLE
  • from Radiomuseum.org
  • Model: Mudlark A205, 20-watt per channel, Class A2 triode amplifier - Silicon Chip Publications Pty.
  • Shape
  • Tablemodel, Box - most often with Lid (NOT slant panel).
  • Notes

  • The Mudlark A205 is a 3-stage lower-powered single-ended design using two paralleled triode-connected beam power pentodes. It also does not use a conventional output transformer but uses a choke as the combined plate load for the triodes, with the output signal being capacitively coupled to a 100 V transmission line transformer. Other novel features include positive drive (class A2) via an emitter follower to the grids of the output valves and quite a complex power supply which includes protection for the valves.

    The A2 designation stands for class A2 operation. This refers to class-A which involves positive drive to the grids of the output valves on positive signal peaks for increased efficiency and higher power (sometimes called "extended" class-A in valve literature).

    The circuit is unconventional because of the emitter follower used to drive the grids of the output valves and in the use of a choke as the plate load instead of a conventional output transformer.

    The circuit is a “parafeed” configuration which uses a relatively low-cost high impedance choke as the load for the plates of the output valves and a capacitor to couple the audio signal to the primary of the output transformer. As a result, there is zero DC in the primary winding, so the output transformer can be much smaller and lower in cost without sacrificing quality.

    It also incorporated a delayed B+ soft start circuit.

    The Mudlark A205 comes in two parts, the main amplifier, and the separate transformer power supply box.

    Designed by David Whitby and published as a kit in Silicon Chip, August & September 2005.

    Specifications:

    Output power:  20 watts per channel into 8Ω
    Input sensitivity:  360mV for 10W into 8Ω
    Signal-to-noise ratio:

     67dB unweighted (22Hz to 22kHz); -91dB A-weighted, both with respect to 20W into 8 Ω.
    Harmonic distortion:  typically, <1.5% at listening levels.
    Frequency response:    ±3dB, 12Hz-57kHz
    Damping factor:  >6 with feedback, >2 without.

     

  • Mentioned in
  • -- Original prospect or advert (Silicon Chip, August & September 2005.)
  • Author
  • Model page created by Gary Cowans. See "Data change" for further contributors.

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