MRC-67A Amplifier-Speaker

© Brooke Clarke 2011

When a radio that works fine as a backpack is used in a vehicle an amplified speaker is needed.  Many of these are designed for a specific radio system and others like the MRC-67A is a Commercial Off The Shelf (COTS) product that has general applicability.

I got these one because it has a broken connector so needs a repair and some reverse engineering.

There are two volume controls, one for the loudspeaker and one for a handset like the H-250.  I haven't tested it, but I've read that when the DC supply is off the handset is directly connected to the radio and will continue to work.  For mobil ops it may be easier to use the M-80 microphone.

ON/OFF Toggle switch HANDSET U-229 type audio POWER Chassis: 2 mail pin Cable: MS3116 F8-2S A: +10 to 36VDC B: Gnd V ma 10 43 24 19 36 15 AUDIO Chassis: MS3114 E10-6P                 (PT07A-10-6P) Cable: MS3116 F10-6S Color Desc U-2291 A Grn Gnd A B Blu Audio In D C Yel PTT C D Vio Audio Out D E Red +DC Pwr n.c. F Blk DC Gnd n.c. Note 1: cable for use with most radios. Handset Volume Top knob Speaker Volume Bottom knob Green LED DC Power good Yellow LED Receive Audio Present

Speaker Enclosure

Chassis Enclosure

Amplifier

There are 4 captured screws in the very corners that hold the two chassis boxes toghther.  They are either 6-1.0 x 35mm or 1/4-28 x 1-3/8" (the screw fits both screw checkeers).

These screws do not fit the two tapped holes (see Controls & Connectors above) on the face where the connectors are located  or the two tapped holes that are directly opposite them.  They may have a center to center distance of 73.675mm (2.900").
It's not clear how the two tapped holes are used.

On the bottom there are four 7.2mm (0.283") I.D. clearance holes in a rectangular pattern that's 82mm (3.23") wide x 106mm (4.17") high.  The idea is to remove open the two boxs and install mounting bolts to hole the connector (rear) box to a bulkhead then reinstall the speaker (front) box.

The back of the speaker has these patent numbers:
3898393 Magnet Centering Device and Shield, C.B. Digre, Aug 6 1975, 335/231; 381/420
4293741 Magnet Assembly, C.B. Digre, Oct 6, 1981, 381/420; 335/231; 381/189; 381/396