The signal and signal intercommunication amplifiers covered by this specification will be used in receiver and tanker aircraft employing aerial refueling boom or receptacle equipment and in the ground support equipment necessary for these applications. Care should be taken to insure the use of the proper class of unit in a given installation.

The following are general installation instructions:

a. Mounting interface

(1) To replace a D7A/B signal amplifier with an M38449-1, -2, -3, or -4, remove the D7A/B and drill three holes in the electrical connector end of the mount base (MT70) in accordance with figure 1 herein and the applicable technical orders. The electrical connectors of the M38449-1, -2, -3, -4 shall be oriented in the same direction as the D7A/B connector and shall be centered on the base within 0.75 inch from the connector end of the base.

(2) To replace an A20-1A/B signal amplifier with an M38449-1, -2, -3, or -4 remove the A20-1A/B and mount tray (base) and install the replacement signal amplifier using the same three mounting holes and screws.

NOTE: The M38449-1, -2, -3, and -4 amplifiers are directly interchangeable with the exception of the electrical connector (see b.(2) below).

b. Electrical connector interface

(1) D7A/B and A20-1A/B signal amplifiers are directly interchangeable with the M38449-1.

(2) Replacing D7A/B and A20-1A/B signal amplifiers with M38449-2, -3, or -4 units requires changing the aircraft connector plug to a M83723-75R1212N, or using an adapter supplied with the signal amplifier.

c. Air vehicle intercom interface (For Information Only)

(1) Replacing D7A/B, A20-1A/B, M38449-1, or M38449-2 signal amplifiers with an M38449-3 or -4 unit requires connecting pin 9 to the audio portion of the aircraft intercom system and, when the aircraft is so equipped, pin 12 to audio common. Pin 11 shall be connected to 28V dc for tanker-receiver intercom operation when the signal amplifier override mode of operation is used. For aircraft not having an override mode, check the appropriate technical orders for termination of pin 11. CAUTION: Once an M38449-3 or -4 signal amplifier has been installed, it must not be replaced with an M38449-1 or -2 without disconnecting pin 9. If this is not done, 28V dc will be applied to the aircraft intercom system since this is a normal output from pin I/9 of M38449-1 and -2 signal amplifiers during the contact and disconnect modes. In addition, pin 10 on class 4 units provide a push-to-talk feature. This pin should be connected to the push-to-talk microphone switch directly for push-to-talk operation only, or through a diode for both push-to-talk and voice operated switching operation. This information does not constitute authorization to perform a modification to an aircraft. Authorization shall be made only by technical orders or contract directive.

NOTE: All diodes contained in the aerial refueling signal circuitry external to the signal amplifier must be removed prior to M38449-3 and -4 installation since the M38449-3 and -4 amplifier is equipped with a special diode for voice communications. M38449-1 and -2 amplifiers also contain standard diodes and do not require external aircraft-mounted diodes to protect the signal circuitry.