60-04-01 BENDIX: Amendment 107 Part 507 Federal Register February 20, 1960. Applies to All Aircraft Public Address Speaker Systems Using the Bendix MI-51B Amspeaker, Serial Numbers 1001 To 1201, Which Have Carbon Resistors in Parallel With or in Lieu of Wire Wound Resistors R-103 and R-106. (Serial Numbers 1001 To 1051 May Have Been So Modified In Service.)
Compliance required by June 1, 1960.
Failures have occurred where the speaker cone of the MI-51B was destroyed by fire as a result of overheating of these carbon resistors, thus creating a possible hazardous condition. Due to the seriousness of the fire hazard associated with these failures, any carbon resistors paralleled with or substituted for resistors R-103 and R-106 shall be removed in accordance with either of the following methods:
(a) Method No. 1. Clip out 3.9 ohm carbon resistors connected across wire wound resistors R-103 and R-106. (Removal of these resistors will reduce the audio output by approximately 10 percent.)
(b) Method No. 2. Replace each of the parallel networks composed of 3.9 ohm carbon resistors in parallel with wire wound resistor R-103 and R-106, with a 0.75 ohm wire wound resistor (plus-minus 5 percent, 1/2 W).
(Bendix Service Bulletin No. M-273 dated July 8, 1959 covers the same subject.)