12 W Amplifier A12

Lowther Manufacturing Co; Kent

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  • Year
  • 1936
  • Category
  • Audio Amplifier or -mixer
  • Radiomuseum.org ID
  • 340685

 Technical Specifications

  • Number of Tubes
  • 6
  • Main principle
  • Audio-Amplification
  • Wave bands
  • - without
  • Power type and voltage
  • Alternating Current supply (AC) / 50-60 Hz 200 - 250 Volt
  • Loudspeaker
  • - This model requires external speaker(s).
  • Power out
  • 12 W (unknown quality)
  • Material
  • Metal case, TUBES VISIBLE
  • from Radiomuseum.org
  • Model: 12 W Amplifier A12 - Lowther Manufacturing Co; Kent
  • Shape
  • Chassis only or for «building in»
  • Dimensions (WHD)
  • 12 x 10.25 x 14 inch / 305 x 260 x 356 mm
  • Notes

  • Type A12 Amplifier

    The speech input from the tuner chassis (or feeder unit, when used separately) is fed to one MHL4 which feeds one output, and simultaneously the other MHL4 which in turn feeds the second output valve.
    The input to the second MHL4 is controlled and at unity amplification, acts simply as a phase reversal stage.

    A jack across a low resistance in the common lead to the output stage enables a pair of phones to be plugged in and the control on the second MHL4 turned until any signal in the phones disappears.

    Amplification in the two chains is then equal and opposite in phase. Separate variable bias resistors are provided in each stage.

    The RC coupling arrangements are calculated for freedom from distortion, rather than high gain, the coupling condenser being of mica dielectric.

    If this amplifier is required separately, either an extra valve can be fitted, or a feeder stage supplied at a cost of 30/ -. Full output can then be obtained from a carbon microphone of normal sensitivity.

    Of the two separate rectifiers, MU14 supplies 450 volts at 120 mA for the output stage alone. While the MU12 gives 410 volts at 100 mA for the LF and radio unit.

    Fuses are provided on both secondary windings as well as on the primary side and a "buffer" condenser is fitted on the MU12 circuit tested at 2,500 volts.
    Smoothing on both lines is carried out by high inductance chokes together with 8 µF surge-proof condensers of the electrolytic type.

    There is a difference of 60 volts between the HT - line, and earth (MU12 circuit only) for the special AVC circuit used in our ADT tuner.

    The amplifier is suitable for PA work as it will fully load two Voigt speaker units, the output transformer being tapped for one or two such units.

    A two-pin socket is provided across the mains input for running a motor or field supply rectifier.

    Specifications

    Power Output 12 watts approximately.
    Output for radio tuner: 300 V, 40 mA  and  4 V, 8 A

  • Price in first year of sale
  • 27.30 GB £
  • Mentioned in
  • - - Manufacturers Literature (Lowther Voigt Radio, Season 1936-37, Page 12.)
  • Author
  • Model page created by Gary Cowans. See "Data change" for further contributors.

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