The Harvey-Wells T-90 Bandmaster is a versatile VFO and crystal controlled, bands witching transmitter designed for use in mobile, portable or fixed installations. It provides RF output on all amateur frequency bands from 3« 5 to 29.7 mcs , inclusive. The maximum input to the PA stage is 90 watts, CW-ICAS, or it may be operated phone with an input of 75 watts maximum«. The RF section consists of an oscillator stage followed by two amplifier-multiplier stages which provide excitation to the final amplifier stage. The oscillator is of the variable frequency type but may be operated crystal controlled as an alternative» The VFO dial scale is calibrated*to the output frequencies. A three position tap switch in the second multiplier stage permits adjustment of the PA grid drive by varying the screen voltageo A protective clamping circuit is provided to hold down the screen of the Power Amplifier should excitation fail. The PA plate is coupled to a Pi network output circuit which is designed to work into a wide range of antenna load impedances. The modulator system includes a speech amplifier stage followed by an amplifier-driver stage which supplies driving voltage to push“ pull modulators. An internally located two position slide switch modifies the speech input so that either carbon, crystal, or high impedance dynamic microphones may be used· When using carbon microphones, microphone button voltage is automatically developed in the speech tube cathode The overall modulation system is designed for maximum response in the speech range for increased side-band power. The T~90 Bandmaster is a complete transmitter, factory wired and tested, including tubes, less power supply«. Some of the special features are: a. TVI Suppression b. Receiver Muting or Disabling c. Remote Control Connections d. Push-to-Talk Operation e. Zero Beating without Carrier On f . Antenna Changeover Relay The heater system of the T-90 is wired in a balanced series- parallel arrangement and filaments may be operated with either 6 or 12 volts AC-DC input simply by properly wiring the power input connector for the correct operating voltage.