|Field Telephone Amplifier No1
Purpose and facilities
The Amplifier Field Telephone No. 1 is a single stage amplifier designed to extend the working range of army field telephones. The direction of amplification is controlled by a switch and “over-over” working is therefore necessary.
The amplifier, contained in a sealed, waterproof case, is suitable for use in tropical climates and is carried together with its battery in a canvas haversack.
The amplifier is not suitable for use on carrier or repeatered channels.
The amplifier is designed to accept the speech output of a Telephone Set F or L without overloading. If used in conjunction with a high output telephone such as the Telephone Set J, the amplifier would overload.
An attenuator is therefore provided inside the case, which is normally strapped out, but the links are removed when the amplifier is used with the Telephone Set J.
Range of working
The range of working using an amplifier at each end of the circuit is approximately 27 to 40 miles of D8 twisted cable depending on whether the cable is wet or dry.
The corresponding figures for D3 cable are 19 to 30 miles.
Controls and connections
The receive gain of the amplifier can be regulated by the volume control marked
REC. GAIN; this control is only operative when the switch is at REC. The switch must always be restored to this position after conversation is over, otherwise no ringing
indication will be received and also the useful life of the battery will be appreciably shortened.
Connection to the telephone is made by means of a twin connector attached to the amplifier panel, while a 5-point connector at the bottom of the case is plugged into the battery.
Battery, dry HT/LT 150/3V No. 3 or Battery, dry HT/LT 162/3V No. 2 or No. 1 may be used.