100-Watt C.W. and Telephony Transmitter

Eddystone (Brand), Stratton and Co., Ltd., Eddystone Radio Ltd.; Birmingham

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  • Year
  • 1935
  • Category
  • Kit (Parts plus instruction) or building instructions only
  • Radiomuseum.org ID
  • 355309

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

 Technical Specifications

  • Number of Tubes
  • 11
  • Main principle
  • Transmitter
  • Wave bands
  • Short Wave (SW only)
  • Power type and voltage
  • Alternating Current supply (AC)
  • Loudspeaker
  • - - No sound reproduction output.
  • Material
  • Metal case
  • from Radiomuseum.org
  • Model: 100-Watt C.W. and Telephony Transmitter - Eddystone Brand, Stratton and
  • Shape
  • Chassis only or for «building in»
  • Notes

  • Technical Description of 1935, 100-Watt C.W. and Telephony Transmitter

    General Description:
    This 1935 transmitter offers crystal-controlled operation for both telephony (voice) and continuous wave (C.W.) transmission. It operates directly from AC mains power and delivers a full 100 watts of RF power output.

    Frequency Selection and Band Switching:

    • Two crystal oscillators are provided, selectable by a switch.
      • Crystal 1: Provides a master frequency in the 3.5 MHz band (80 metres)
      • Crystal 2: Provides a master frequency in the 7 MHz band (40 metres)
    • Interchangeable coils (L3, L5, L9) are used for each band and stage.
      • 80 metres: Crystals 1 & 2 offer dedicated coils for oscillator, buffer, and final amplifier stages.
      • 40 metres: Crystals 1 & 2 require coil changes for all stages.
      • 20 metres:
        • C.W. operation achieved by changing only L3 and L5 (using Crystal 2), resulting in 40, 20, and 20 metre operation respectively (buffer stage doubles frequency).
        • Telephony operation requires an additional 14 MHz crystal (not commonly used).

    Circuit Stages:
    The transmitter is housed in three separate units:

    Unit A - Crystal Oscillator & Buffer Amplifier

    • Master oscillator valve: Osram PT4 pentode (V5) - high output for low HT voltage.
    • Crystal oscillator utilizes a 6-pin interchangeable coil for frequency selection.
    • Buffer amplifier: Mullard T25D valve (V4) - metallised, class C operation for full telephony modulation.
    • Both stages receive HT power (500 volts) from the subsidiary power supply in Unit C.
    • Grid bias for both buffer and output stages sourced from a dedicated 250-volt power supply mounted under Unit A's baseboard (diagram 3).
    • Mullard DW2 rectifier valve (V6) provides bias voltage.
    • CW operation key jack for grid blocking.
    • Provision for a coupling coil for Zepp-fed Hertz antenna.

    Unit B - Main Power Supply

    • High voltage rectification: Two Osram GUI (V1 & V2) mercury-vapor rectifier valves for full wave rectification.
    • High high-voltage transformer located on the right side.
    • Smoothing circuit employs two heavy chokes in series with three reservoir capacitors.
    • Separate transformer for heating the GUI rectifiers (primary and secondary windings require high insulation).
    • Load resistor (R16) across HT output for peak voltage reduction and improved regulation.
    • Main power switch controls all three units.
    • Dedicated control switch for Unit B allows independent power control for the remaining transmitter sections.

    Unit C - Subsidiary Power Supply (not explicitly detailed)

    • Provides 500-volt HT power for Unit A stages.

    Additional Notes:

    • Worldwide range achievable (limited by atmospheric conditions).
    • 80 metres preferred for local communication due to skip distance of 40 metres (varies seasonally).
    • Milliammeters monitor current in each stage for simplified tuning.

    Overall, this 1935 transmitter offered a versatile and powerful solution for both voice and CW communication at the time.

  • Mentioned in
  • - - Manufacturers Literature (Eddystone Shortwave Manual No. 2 1935, Pages 42 - 48)
  • Author
  • Model page created by Gary Cowans. See "Data change" for further contributors.

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