UHF radio and audio adopter

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i am using military radio ARC164. i have adopters MX1646A/AIC nsn 5965001683608 and MX1646B/AIC nsn 5965010178741. The two are given as substitute of each other onthe net . but they are not working out with me. i replaced A type with the B type but B type only gave me noise and no audio. Can some body give me the difference between the two? can some one send me the circuit diagrams or technical specs. i will be a lot grateful.