CROSS-REFERENCE 
     The lightweight headset shown in this application may be of the type shown and described in greater detail in my copending application Ser. No. 555,529, filed Mar. 5, 1975, now U.S. Pat. No. 3,971,901, entitled &#34;Communications Headset with Reversible Mounting Means.&#34; 
     BRIEF SUMMARY 
     Lightweight telephone operator headsets of the prior art have commonly required amplifiers in order for the output of the headset microphone to be compatible with conventional telephone switchboard apparatus. It has therefore been the practice to supply each headset with a permanently connected amplifier. 
     In the apparatus of the present invention the light-weight operator&#39;s headset is part of a headset module. The headset module includes a microphone, an earpiece, an earphone transducer, necessary supporting elements, and a cable connecting the microphone and the earphone transducer to a connector plug 13, which is also part of the headset module. 
     A station module includes an amplifier, a receptacle adapted to cooperate with the plug of the headset module, and a second connector plug adapted for insertion in a conventional switchboard. The amplifier and the receptacle are parts of the same rigid assembly. The second connector plug may be part of the same assembly through flexible conductors. The assembly may also include other elements, e.g., a control switch. 
     With this arrangement, a station module is provided for each switchboard station, rather than having an amplifier for each operator&#39;s headset. In any given installation, the number of switchboard stations is substantially smaller than the number of operators, so that a considerable economy of equipment is achieved. 
     The plug on the headset module and the receptacle on the station module together form an electrical connector which is lockable and manually releasable. Hence, the plug connector cannot become accidentally loosened or separated from the receptacle due to movements of the operator in the neighborhood of the switchboard station. Two latch members are provided on each plug and both must be manually released in order to separate the plug from the receptacle. 
    
    
     DRAWINGS 
     FIG. 1 is a perspective view showing an operator wearing a headset module including a connector plug and a station module including a receptacle for the connector plug and another connector plug adapted for plugging into a switchboard. 
     FIG. 2 is a view partly in elevation and partly in section, showing the station module appearing in FIG. 1, on a larger scale. 
     FIG. 3 is a view, partly in plan and partly in section on the line 3--3 of FIG. 2, showing the station module. 
     FIG. 4 is a right-hand view of the station module of FIGS. 2 and 3. 
     FIG. 5 is a left end elevational view of a connector plug forming part of the headset module of FIG. 1. 
     FIG. 6 is a plan view of the connector plug of FIG. 5. 
     FIG. 7 is a sectional view taken along the line 7--7 of FIG. 6. 
     FIG. 8 is a view partly in elevation and partly in section, showing the connector plug of FIGS. 5-7 assembled with the receptacle of FIGS. 2-4, with the receptacle shown in section. 
     FIG. 9 is a perspective view on an enlarged scale showing a latch plate used in the receptacle. 
     FIG. 10 is an elevational view showing a switch control case used in a modified form of station module embodying the invention. 
     FIG. 11 is a plan view of the switch control case of FIG. 10, with certain parts shown in section. 
     FIG. 12 is a right-hand elevational view of the switch control case of FIG. 11. 
     FIG. 13 is a perspective view showing another embodiment of a switch control case usable in a station module constructed in accordance with the invention. 
    
    
     DETAILED DESCRIPTION 
     HEADSET MODULE 
     FIG. 1 
     FIG. 1 shows an operator wearing a headset including a yoke 1 extending over the top of the head and terminating in a pair of pads 2, only one of which is seen in the drawing. A boom 3 extends forwardly from the pad 2 and supports at its forward end a housing 4 which encloses an earphone transducer. An acoustic path extends from the earphone transducer through a tube 5 to an earpiece 6 in the operator&#39;s ear. A microphone 7 is supported at the end of a curved conduit 10, whose opposite end is supported on the housing 4 by an electrical connector including an articulated plug assembly 11. Conductors connected to the earphone transducer and to the microphone 7 extend into the housing 4 and thence through a flexible cable 12 to a connector plug 13. The headset includes the yoke 1, pads 2, boom 3, housing 4, tube 5, earpiece 6, conduit 10, microphone 7 and plug assembly 11. The headset module includes the headset plus the cable 12 and connector plug 13. 
     STATION MODULE 
     FIGS. 1-4, 8 AND 9 
     The connector plug 13 is insertable into a connector receptacle 14 formed on one end of a station module 15. The other end of the station module 15 carries a pair of projecting coaxial connector elements 16, adapted for insertion in a conventional switchboard. The station module 15 includes a housing 17 enclosing an amplifier shown diagrammatically at 18 (FIGS. 2 and 3). 
     The station module 15 includes an upper casing part 20 and a lower casing part 21 held together by screws 22 or other suitable retaining devices. The terms &#34;upper&#34; and &#34;lower&#34; are used simply for convenience with respect to the orientation of the station module as shown in FIG. 2. It should be understood that the station module may be used in any other orientation. The housing 17 is attached to the under side of the upper casing part 20 by means of screws 19, or other suitable retaining devices. The receptacle 14 includes part of the upper casing part 20 and all of the lower casing part 21. Receptacle 14 has a recess 14a formed in its end. The inner end 14b of the recess 14a serves as a seat for the plug 13. A plurality of electrically conductive connector elements, shown as pins 23, are fixed on the seat 14b by being molded in an insulating block 24 (FIG. 3) having flanges 24a (FIG. 3) received in grooves 21a formed in the casing part 21. A pair of guide pins 25 are also molded in the block 24. The block 24 defines part of the inner end of recess 14a. 
     Each of the casing parts 20 and 21 has one complete side wall 20e, 21e, and two partial side walls, 20f, 21f. The side walls 20e, 21e, 20f, 21f together define the sides of the recess 14a. Each of the side walls 20e, 21e has a plane inner surface with a broad indentation 20b, 21b (FIG. 4) therein, and a notch 20g, 21g at the bottom of the indentation. A latch plate 26, best seen in FIG. 9, is received in each of the indentations 20b, 21b and comprises a generally rectangular frame with a bridging member 26a extending across the frame. Each of the casing parts 20 and 21 has a post 20c, 21c formed integrally therewith and projecting through the aperture 26b between the bridging member 26a and the innermost side of the latch plate 26. The parts 20 and 21 also include transverse walls 20h, 21h (FIG. 2) on which the block 24 is fixed. Spacer blocks 27 of sponge rubber or the like are bonded to and fill the spaces between the posts 20c, 21c, and the facing surfaces of the transverse walls 20h, 21h, so as to hold the latch plates 26 in place in the indentations 20b, 21b. The partial side walls 20f, 21f of the casing parts 20 and 21 are provided with shoulders, as shown at 21d in FIG. 3. The shoulders 21d, the post 21c, the corresponding shoulders and post of the upper casing part 20, and the insulating block 24, together define the inner end of the recess 14a. Cushion strips 30 (FIGS. 2-4) of sponge rubber or the like are bonded at their ends to the shoulders such as 21d as well as to the posts 20c, 21c. 
     Wires 28 (FIG. 3) extend from the inner ends of the connector pins 23 through openings in the facing ends of the casing part 21 and the housing 17. The wires may also be accommodated in the open under side of the casing part 20. Two of the wires lead to the input terminals (not shown) of the amplifier 18. The output terminals of the amplifier are connected to the center tips 16a of the coaxial connectors 16. The other two wires 28 are connected, possibly through circuit elements in the housing 17, to the sleeves 16b of the connectors 16. 
     CONNECTOR PLUG 
     FIGS. 5-8 
     The connector plug 13, shown in detail in these figures, includes a set of electrically conductive connector elements 31, shown as hollow receptacles for receiving the pins 23 in the receptacle 14. The connector elements 31 and a pair of guide sleeves 36 are molded into a block 32 which is fixed between the upper and lower casing halves 33, 37 of the plug 13. Two latch members 34 are movably supported on the plug 13. Each latch member 34 has a latch tooth 34a and an operating segment 34b. Each casing half is provided with apertures through which the tooth 34a and the operating segment 34b project Between those apertures, bridging portions 33a, 37a of the casing halves 33, 37 extend across the latch members 34. Each latch member has a finger 34c on its outer side at its right-hand end, as viewed in FIG. 7, which engages the outside of the casing half 33, 37 and prevents the latch member 34 from moving into the cavity defined by the hollow casing halves 33, 37. 
     The latch members 34 are biased to their outer or latching positions, seen in FIGS. 5-7, by means of broad U-shaped leaf springs 35. The ends of each leaf spring 35 are bent over and engage a surface of the block 32. The middle of each leaf spring 35 engages the inside of one of the latch members 34. 
     As the connector plug 13 is moved to engage the receptacle 14, the latch teeth 34a are forced inwardly into the cavity in the connector plug 13 when they engage the transverse frame member 26c (FIG. 9) of the latch plate 26. The leading end of each latch tooth 34a is beveled so that it slides past the transverse frame member. After the latch teeth 34a slide past transverse frame member 26c, they are moved outwardly by their associated springs 35 so that the square shoulder at their right-hand ends, as viewed in FIGS. 7 and 8, moves into the opening 26d in the latch plate 26, thereby locking the connector plug 13 firmly to the receptacle 14. The cushion strips 30 are compressed when the plug 13 is in its latching position, and bias the plug outwardly so that the latch teeth 34a are held in firm engagement with the latch plate 26. The connector plug 13 cannot then be removed from the receptacle 14 by pulling on the cord 12 at its right-hand end. In order to separate the plug 13 from the receptacle 14, the two operating segments 34b of the latch members 34 must be depressed, i.e., forced inwardly toward the cavity in the connector plug 13, thereby moving the latch teeth inwardly and releasing the latch teeth from the latch plate 26, so that the plug 13 may be withdrawn. 
     The casing halves 33, 37 are provided with abutting ridges 33b, 37b (FIG. 5), which together form a projection receivable in a groove 14c formed in one side of the receptacle 14. This projection is a polarizing key which prevents improper orientation of the plug 13 when it is inserted into the receptacle 14. 
     FIGS. 10-12 
     These figures illustrate a modification of the station module according to the invention, including a switch control case 40, in which the receptacle 14 is located at the right-hand end of the case. A connecting cable 41, which leads to a connector (not shown) having connecting elements similar to the connecting elements 16 of FIG. 1, is located at the same end of the case 40 as the receptacle 14. A spring clip 42 is attached to the housing of the case 40 by means of screws 43. A link 44 engages a hole in the spring clip 42. A loop 45 engages the link 44, and is adapted for hanging either on the wrist of the operator, or on a suitable hook on the switchboard. The link 44 and loop 45 are omitted from FIGS. 11 and 12. A push-to-talk switch 46 is provided on the case 40. 
     The clip 42 may be used to hang the case from a belt or pocket of the operator&#39;s clothing, or it may be used to hang the case on a suitable support on the switchboard station. 
     FIG. 13 
     This figure illustrates another switch control case 50, which differs from the case 40 of FIG. 12, in that the connector plug 13 and its associated receptacle 14 (not shown in FIG. 13) are at one end of the case, and a cable connection 51 to the switchboard is at the opposite end of the module.
This telephone apparatus includes a headset module and a station module. The headset is of a lightweight type which requires an amplifier for the electrical signal produced by the microphone, in order for the output signal to be compatible with conventional telephone switchboard apparatus. The headset module also includes electrical conductors extending from the microphone and earphone of the headset to a latchable plug forming part of a connector. The station module includes a receptacle for receiving the latchable plug, an amplifier and a connector plug engageable with a conventional receptacle. That connector plug may be part of a rigid assembly including the other parts of the station module, or it may be connected to that assembly by flexible conductors.