Type 49131 Loudspeaker-Amplifier Aboard Pampanito.
Type 49131 Loudspeaker-Amplifier Aboard Pampanito.


Power required for operation.-Unit operates from a power source of 115 volts +-10 percent either d.c. or 60-cycle, single phase a.c. The power consumed is not more than 50 watts.

Description.-The loudspeaker-amplifier unit is designed for use with radiotelephone communication in connection with Naval radio receivers. Each unit contains a loudspeaker proper, a power amplifier, and the necessary rectifier and filter equipment for its operation from the power or lighting circuits of the vessel upon which it is installed.

The unit is designed to withstand continuous simple harmonic vibration, having an amplitude of 0.03135 inch at frequencies between 5 and 30 cycles per second, except at the critical frequency of the whole unit at which frequency it withstands this vibration for one minute.

Each unit consists of a push-pull power amplifier suitable for raising the level of a standard input of 6 milliwatts at 600 ohms to a level of at least 1.75 watts at 15 ohms for feeding the voice coil of a loud speaker, a rectifier to permit the operation of the unit on 115 volts a.c. or d.c. and a permanent field, cone-type dynamic loudspeaker, all housed within a spray-proof cast aluminum cabinet suitable for bulkhead mounting.

The cabinet is provided with a reinforced cast aluminum mounting cover and mounting lugs or bosses at each corner to permit securing the unit to a bulkhead. The loudspeaker and the necessary controls for the operation of the unit are mounted on the front panel (cover) of the unit. The chassis mounts all the necessary amplifier and rectifier equipment and is secured to the mounting brackets carried by the cover through shock-proof mountings

The loud speaker is of the dynamic cone type, employing a permanent magnet for the field. It is capable of handling up to 1.75 watts without appreciable variation in fidelity. The diaphragm of the speaker is protected from both mechanical and acoustical damage from the blast of gun fire by a blast plate and durable diaphragm construction. The voice coil impedance is 15 ohms.

The amplifier-power unit consists of the following basic components:
1. An input transformer
2. A push-pull power amplifier.
3. An output transformer for feeding the loud speaker voice coil.
4. A rectifier with the necessary filter capacitors and reactors.
5. A switch for changing form a.c. to d.c. operation.
6. Necessary capacitors, resistors, etc.

An a.c./d.c. switch is provided on the amplifier chassis. In the d.c. position the rectifier tube plate-cathode circuit is shorted and at the same time the heater is shorted and a suitable resistor connected in the series heater circuit combination to permit the maintenance of the proper operating current for the amplifier tube heaters and pilot lamp.


           Tube complement
   Function         of tubes  Type
Power amplifier         2     35L6GT
Rectifier               1     35Z5GT
 Total                  3
Input impedance.-600 ohms +-10 percent at 1,000 cycles for any input level up to 6 milliwatts and any adjustment of the volume control.

Gain.-The maximum amplifier gain is such that with an input of 6 milliwatts at 1,000 cycles the output to the loud speaker voice coil is at least 1.75 watts. The manual gain control operates in such a manner as not to appreciably affect the fidelity characteristics of the amplifier speaker, introduce distortion or change the input impedance of the units. It effects a variation of output (for constant input) of at least 40 decibels. The attenuation offered versus angular dial rotation is linear in decibels within plus or minus 12 decibels.

Distortion.-With a sinusoidal input and with an output of 1.75 watts to the loudspeaker voice coil, the total distortion is less than 10 percent.

Frequency.-The frequency characteristics of the amplifier is "flat" within 2 decibels between the limits of 300 and 5.000 cycles with reference to the 1,000 cycle response.

The over-all frequency characteristics of the units, measured as acoustical output with respect to a standard input of 6 milliwatts, is flat within 6 decibels over a frequency range of 750 to 1,300 cycles. The acoustical pressure averages at least 10 dynes/cm squared.

Hum and noise level.-The total hum and noise level of the unit as measured electrically at speaker voice coil with no signal impressed on the input is at least 50 decibels below the rated maximum output of 1.75 watts.

      Weights, dimensions, and Navy type numbers
    Unit         Height  Width   Depth  Weight
                 Inches  Inches  Inches           
Loudspeaker    14 49/64  14 1/4  8 1/4  <50 pounds.


The information enclosed here is excerpted from:
Catalogue of Naval Electronic Equipment-April 1946- NavShips 900,116.


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Version 2.00, 11 Sep 2006