US2427496A

US2427496A - Intercommunication system

Info

Publication number: US2427496A
Application number: US625152A
Authority: US
Inventors: Feldscher Willard
Original assignee: GOLDFIELD CONS MINES Co
Current assignee: GOLDFIELD CONS MINES Co; GOLDFIELD CONSOLIDATED MINES Co
Priority date: 1945-10-29
Filing date: 1945-10-29
Publication date: 1947-09-16
Anticipated expiration: 1964-09-16

Description

Sept. 16, 1947. w. FELDSCHER INTERCOMMUNICATION SYSTEM Filed Oct. 29, 19 .5 4 Sheets-Sheet 1 lb III Av wmfi Z: 1 II II Z; Q- wwmo. N: F0- I I I l III III LIL I NH E I 2 I INVENTOR.

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WILLARD FELDSCHER Sept. 16, 1947. w. FELDSCHER INTERCOMMUNICATION SYSTEM Filed Oct. 29, 1945 4 Sheets-Sheet 4 INVENTOR. WILLARD F'ELDSCHER Patented Sept. 16, 1947 ZAZ'ZAit INTERCOMIVIUNICATION SYSTEM Willard Feldscher, San Mateo, Calif., assignor to The Goldfield Consolidated Mines Company, San Francisco, Calif., a corporation Application October 29, 1945, Serial No. 625,152

12 Claims.

Thi invention relates to intercommunicating apparatus in general, and more particularly to intercommunicating systems comprising a plurality of stations; each station including a transducer usable both as a transmitting microphone and as a loud-speaking receiver.

An object of this invention is to provide an improved intercommunicating system comprising a plurality of stations; each stationincluding a transducer operable either as a transmitting microphone or as a loud-speaking receiver and an amplifier.

Another object of this invention is to provide an improved intercommunicating system comprising a plurality of stations; each station including a transducer operative selectively as a transmitting microphone and as a loud-speaking receiver, and an amplifier adapted to function as a voltage amplifier when the associated transducer function as a microphone and to function as a power amplifier when the associated transducer functions as a loud-speaking receiver.

A further object of this invention is to provide an intercommunicating system comprising a plurality of stations; each station including a transducer operative selectively as a transmitting microphone and as a loud-speaking receiver and an amplifier; the amplifier at each station comprising only a part of the total amplification available to that station.

Still another object of this invention is to provide an intercommunicating system comprising a plurality of stations, each of the stations having an amplifying device, and connections between the amplifying devices, whereby the amplifying devices are enabled to function as parts of an amplifying unit during communication between the stations.

Other and further objects will be apparent to those skilled in the art to which this invention relates from the following specification and drawings.

Referring to th drawings briefly, Figs; 1 and 2, taken together, illustrate an intercommunicating system embodying the present invention; Fig, 1 illustrating diagrammatically the apparatus disposed at a station A incorporated in the system, and Fig. 2 illustrating diagrammatically the apparatus disposed at a station B incorporated in the system.

Figs. 3 and 4, taken together, illustrat a modified form of the intercommunicating system embodying the present invention; Fig. 3 illustrating diagrammatically the apparatus disposed at a station #1 incorporated in the system, and Fig. 4

illustrating diagrammatically the apparatus disposed at a station #2 incorporated in the system.

Referring now more particularly to Figs. 1 and 2 of the drawings, the intercommunicating system there illustrated comprises a plurality of statlons including the stations A and B, provided with apparatus respectively illustrated in Figs. 1 and 2. More particularly, the apparatus disposed at the station A comprises a transducer IOI operative selectively as a transmitting microphone and as a loud-speaking receiver; a combination rectifier and amplifier tube I02; a talklisten key I03; a master switch I00 for connecting th tube I02 to a source of -volt A. C. power supply; and an electric network including a coupling transformer I05 coupling the apparatus at the station A to an associated signalling line I00 extending between each of the stations A, B, etc.

Preferably, the transducer IOI is of any suitable type such, for example, as the electrodynamic or the piezoelectric type; while the tube I02 is of the 117L7GT type incorporating 9, rectifier portion (including an anode I00, a cathode I0! and a cathode heater I03) and a beam power tetrode portion (including an anode I09, a screen grid H0, a control grid III, a cathode II2, beam electrodes I I3 and a cathode heat H4) In the tube I02, the tetrode portion constitutes a voltage amplifier when the transducer IOI is functioning as a microphone, and constitutes a beam power amplifier when the transducer IOI functions as a loud-speaking receiver. Also in the tube I02 the rectifier and amplifier portions ar enclosed in a common envelope I I 5; while the cathode heaters I 08 and H4 are connected in series to the master switch I04.

The talk-listen key I03 is of the conventional four-blade double-throw type, selectively operative between talk and listen positions. Specifically, the talk-listen key I03 comprises four blades IIB, II I, H8 and H9 that are operative together and normally biased to the listen position.

Considering the connection and arrangement of the circuit network in greater detail, one terminal of the transducer IOI is connected through a shielded cable I20 to th blade II6 of the talklisten key I03, and the other terminal of this transducer is connected to the blade II8 of the talk-listen key I03 and to the by-pass capacitor I2 I. The make contact associated with the blade H5 and the break contact associated with the blade I I! are connected to the control grid I II of the tetrode amplifier through the shielded cable I22, which is also connected to the grid leak resistor I23. The sheaths of both of the shielded cables I20 and I22 are grounded to the chassis of the apparatus to reduce stray pickup in the grid circuit of the tetrode amplifier. The break contact of the blade H6 and the make contact of the blade II! are connected to the screen grid IIO of the tetrode and to the filter capacitor I24 and resistor I25 through the conductor I3I. The make contact of the blade H8 and the break contact of the blade I I9 are connected to the bus I26; which is connected to one blade of the master power switch I04, to both of the filter capacitors I24 and I21, and to a terminal of the bypass condenser I28, the other terminal of this latter condenser being grounded to the chassis. The cathode resistor I29 and the cathode resistor shunting capacitor I30 are also connected to the bus I20, together with the lower terminal of the grid leak resistor I23.

The break contact of the blade H8 and the make contact of the blade II9 are connected to the anode I09 of the tetrode amplifier; and the blades III and H9 are connected to the primary winding of the coupling transformer I05, the secondary winding of which is connected to the 'gnalling line I00. The coupling transformer I comprises a portion of an impedance network for matching the apparatus disposed at the station A to the signalling line I00. More particularly, both the transducer I01 and the coupling transformer I05 are adapted to be matched both to the input and to the output of the tetrode amplifier, as explained more fully hereinafter. Specifically, in the circuit control network disposed at the station A it has been found that the following values for the different elements are quite satisfactory:

Filter capacitor I24 mfd Filter capacitor I21 mfd Filter resistor I25 ohms By-pass capacitor I28 mfd Cathode resistor I29 ohms Cathode resistor shunting capacitor I30 mid" 25 Grid leak resistor I23 ohms 250,000 By-pass capacitor I2I mfd 0.005

Similarly, the apparatus disposed at the sta: tion B comprises a transducer 20I operative selectively as a transmitting microphone and as a loud-speaking receiver; a combination rectifier and amplifier tube 202; a talk-listen key 203; a master switch 204 for connecting the tube 202 to a source of 110-volt A. C. power supply; and an electric network including a. coupling transformer 205 coupling the apparatus at the station B to an associated signalling line I00 extending between each of the stations A, B, etc.

Preferably, the transducer 20I is of any suitable type such, for example, as the electrodynamic or the piezo-electrio type; while the tube 202 is of the 11"IL'7GT type incorporating a rectifier portion (including an anode 200, a cathode 201 and a cathode heater 208) and a beam power tetrode portion (including an anode 209, a screen rid 2I0, a control grid 2| I, a cathode 2I2, beam electrodes 2 I3 and a, cathode heater 2 I4) In the tube 202, the tetrode portion constitutes a voltage amplifier when the transducer 20I is functioning as a microphone, and constitutes a beam power amplifier when the transducer 20I functions as a loud-speaking receiver. Also in the tube 202 the rectifier and amplifier portions are enclosed in a common envelope 2I5; while the cathode heaters 208 and 2I4 are connected in series to the master switch 204.

The talk-listen key 203 is of the conventional four-blade double-throw type, selectively operative between talk and listen positions. Specifically, the talk-listen key 203 comprises four blades 2I6, 2I'I, 2I8 and 2I9 that are operative together and normally biased to the listen position.

Considering the connection and arrangement of the circuit network in greater detail, one terminal of the transducer 20I i connected through a shielded cable 220 to the blade 2I6 of the talklisten key 203, and the other terminal of this transducer is connected to the blade MB of the talk-listen key 203 and to the by-pass capacitor 22 I. The make contact associated with the blade 2H5 and. the break contact associated with the blade 2H are connected to the control grid 2I I of the tetrode amplifier through the shielded cable 222, which is also connected to the grid leak resistor 223. The sheaths of both of the shielded cables 220 and 222 are grounded to the chassis of the apparatus to reduce stray pickup in the grid circuit of the tetrode amplifier. The break contact of the blade 2 I6 and the make contact of the blade 2 H are connected to the screen grid 2I0 of the tetrode and to the filter capacitor 224 and resistor 225 through the conductor 23L The make contact of the blade 2 I8 and the break contact of the blade 2 I 9 are connected to the bus 226; which is connected to one blade of the master power switch 204, to both of the filter capacitors 224 and 221, and to a terminal of the by-pass condenser 228, the other terminal of this latter condenser being grounded to the chassis. The cathode resistor 229 and the cathode resistor shunting capacitor 230 are also connected to the bus 226, together with the lower terminal of the grid leak resistor 223.

The break contact of the blade 2I8 and the make contact of the blade 2I9 are connected to the anode 209 of the tetrode amplifier; and the blades 2H and 2H! are connected to the primary winding of the coupling transformer 205, the secondary winding of which is connected to the signalling line I00. The coupling transformer 205 comprises a portion of an impedance network for matching the apparatus disposed at the station B to the signalling line I00. More particularly, both the transducer 20I and the couplin transformer 205 are adapted to be matched both to the input and to the output of the tetrode amplifier, as explained more fully hereinafter. Specifically, in the circuit control network disposed at the station B it has been found that the following values for the difierent elements are quite satisfactory:

Filteg gapacitor 224 mfd 40 Filter capacitor 221 mfd 20 Filter resistor 225 ohms 500 By-pass capacitor "228 mfd 0.1 Cathode resistor 229 oh1ns 500 Cathode resistor shunting capacitor 230 mfd 25 Grid leak resistor 223 ohms 250,000 By-pass capacitor 22I mfd 0.005

Considering now the operation of the intercommunicating system, when the person at the station A wishes to communicate with the person at any other station connected to the system, for example the person at the station B, he merely operates the talk-listen key I03 from its normal listening position to its operated talk position, as illustrated in Fig. 1. This operation of the talk-listen key I03 at the station A causes the transducer IOI'to be operative as a transmitting microphone instead of as a loud-speaking receiver, and causes operation of the tetrode amplifier as a first-stage voltage amplifier instead of as a second-stage power amplifier. It is further assumed that at this time the master switch I04 at the station A occupies its closed position and that the'master switch at the other station, such for example a the master switch 284 at the station B, occupies its closed position.

When the master switch HM at the station A is closed, the source of 110-volt alternating current power supply is connected directly across the series-connected cathode heaters I08 and I I4, whereby the heaters mentioned effect heating of the associated cathodes I01 and H2 in order to render these cathodes electron emissive. Also, closing the master switch I04 applies the 110- volt alternating current to the anode I06 of the rectifier. When the positive half-cycle of the alternating current is applied to this anode I06 current flows between the cathode Hi7 and the anode Hi6, thereby charging the capacitor 121; and at the same time some of this current flows through the resistor 82-5, also partially charging the capacitor 2 1. The current also at this time fiows through the conductor I3! applying a positive potential to the screen grid I ill of the tetrode; and thence through the blade iii of the talkliste-n key I83 to the primary of the transformer Hi5; and from the primary of this transformer E85 through the blade H9 or the talk-listen key 33 to the anode its of the tetrode amplifier, thereby rendering the amplifier operative. When the negative half -cycle of the alternating current is applied to the anode Hi6 of the rectifier, no current flows between the cathode ml and the anode Hi8; and during this half-cycle current for the tetrode amplifier is supplied by the capacitors in and i2? of the filter network, inasmuch as during this half-cycle these capacitors at least partially discharge, thereby applying a positive potential to the conductor I3! and to the screen grid Hill of the tetrode amplifier. Current from the conductor H31 is supplied to the primary of the transformer Hi5 and to the anode I09 of the tetrode amplifier through the aforesaid blades i ii and l 59 of the talk-listen key i 63.

Inasmuch as the transducer it! connected to the grid H! of the tetrode amplifier functions at this time as a microphone, modulated potentials produced by this transducer modulate the electron stream through the tetrode amplifier, and the aforesaid currents flowing from the conductor l3! through the blade ill of the talk-listen key M3, the primary of the transformer H35, and the blade E E9 of the talk-listen key N33 to the anode of this tetrode amplifier are modulated by the action of the grid ill of the tetrode amplifier in accordance with the sound vibrations picked up by the transducer lei. These undulating electric currents produced by the operation of the voltage amplifier are applied to the signalling line I90 by the transformer I05, and they are received from this line by the transformer 205 at the station B and the corresponding transformers at the other stations.

Considering now the operation of the apparatus at one of the stations operating as a receiving station, such for example as the station B, the amplified undulating currents transmitted over the signalling line Hill effect operation of the coupling transformer 205, the primary winding of which is connected to the blades 2!! and M9 of the talk-listen key 203. More particularly, at this time it is assumed that the talk-listen key 283 occupies its normal listen position and that the power switch 204 occupies its closed position, whereby the undulating currents are fed over the shielded conductor 222 connected to the break contact of the blade 2|! to the control grid 2!! of the tetrode amplifier. Undulating currents are also fed from the break contact of the blade 6 2| 9 to the cathode of the tetrode amplifier by way of the conductor 226 and the cathode resistor .229 and cathode resistor shunting condenser 230. These undulating currents are amplified by the tetrode amplifier through the operation of the control grid 2 and its influence on the electron stream between the cathode 2l2 and the anode 209, so that corresponding undulating currents of an amplified order are fed from the anode 209 of the tetrode amplifier through the break contact of the blade 218 to one terminal of the transducer Zfil which is connected to the blade H8. The other terminal of the transducer 20] is connected to the blade 216 and through the break contact of this blade -2l6 to the conductor 23l, which is connected to the screen grid electrode 210 of the tetrode amplifier and to the filter network consisting of the capacitors 224 and 221 and the resistor 225; whereby the transducer 20!, functioning as a loud-speaking receiver, reproduces sounds corresponding to the undulating currents fed thereto.

The rectifier, consisting of the anode 206, the cathode 20! and the cathode heater 2H8, functions in the same manner as the corresponding rectifier disposed at the station A and illustrated in Fig. 1, in that during the interval when the positive half-cycle is applied to the anode 206, current flows between the cathode 201 and the anode 2136, thereby charging the capacitor 221; and at the same time, some of this current flows through the resistor 225, also partially charging the capacitor 224. The current also at this time flows through the conductor 23! as described above. Thus, the transducer 201 functions as a loud-speaking receiver and the tetrode amplifier functions as a beam power amplifier.

Of course it will be understood that in the intercommunicating system after the person at the station A is through talking he may restore the associated talk-listen key 163 to its normal listen position, whereby the station A is converted to a receiving station; and at this time the person at the station B may operate the associated talklisten key 283 to its talk position, whereby the station B is converted to a transmitting station. Further, it will be understood that when any one of the stations is operating as a transmitting station, the associated transducer functions as a transmitting microphone and the associated tetrode amplifier functions as a voltage amplifier; whereas when any one of the stations is operating as a receiving station, the associated transducer functions as a loud-speaking receiver and-the associated tetrode amplifier functions as a beam power amplifier. Finally, it will be appreciated that only one station at any one time may operate as a transmitting station, whereas all of the other stations may operate simultaneously as receiving stations.

Referring now more particularly to Figs. 3 and 4 of the drawings, the modified form of the intercommunicating system there illustrated comprises a plurality of stations, including the station #1 and the station #2, provided with apparatus respectively illustrated in Figs. 3 and 4. More particularly, the apparatus disposed at the station #1 comprises a transducer 3! operative selectively as a transmitting microphone and as a loud-speaking receiver; a combination rectifier and amplifier tube 382; a talklisten key 303; a master switch 304 for connecting the tube 382 to a source of volt A. C. power supply; an impedance matching network including a station selector switch 395; and a 7 home signalling line 35!, accessible to the selector switches at each of the other stations.

Preferably, the transducer 3M is of any suitable type, such for example as the electrodynamic or the piezoelectric type; while the tube 302 is of the 11'7P'7GT type incorporating a rectifier portion (including an anode 306, a cathode 381, and a cathode heater 308) and a beam power tetrode portion (including an anode 309, a screen grid 3l0, a control grid 3, a cathode 3|2, beam electrodes 3| 3 and a cathode heater 3M). In the tube 302, the tetrode portion constitutes a voltage amplifier when the transducer 30I is functioning as a microphone, and constitutes a beam power amplifier when the transducer 395 is functioning as a, loud-speaking receiver. Also, in the tube 302 the rectifier and amplifier portions are enclosed in a common en velcpe 3R5; while the cathode heaters 398 and 3H5 are connected in series to the master switch 394.

The talk-listen key 383 is of the conventional two-blade double-throw type, selectively operative between talk and listen positions. Specifically, the talk-listen key 393 comprises two blades 316 and 3V that are operative together and nor mally biased to the listen position.

Considering the connection and arrangement of the circuit network in greater detail, one terminal if the transducer 3! is connected to the blade 35? of the talk-listen key 3% and the other terminal of this transducer is connected through the bus 326 and the cathode resistor 329 and cathode resistor shunting capacitor 336, to the cathode 3H2, of the tetrode amplifier.

The make contact associated with the blade SIS and the break contact associated with the blade 3H are connected through the impedance network (consisting of the resistor 35!, coupling capacitor $62, and grid leak resistor 3&3) to the control grid 3!] of the tetrode amplifier. The break contact of the blade 31S and the make contact of the blade 3H are connected together and through a coupling capacitor 364 to the anode 389 of the tetrode amplifier. 'The anode 389 of the tetrode amplifier is connected to the screen grid 358 of the tetrode amplifier through the resistor which in turn is connected to the filter network consisting of the filter capacitors 324 and 32'! and the filter resistor 325. The ter resistor 325 and the filter capacitor 32'? are connected to the cathode 397 of the rectifier. The blade of the talk-listen key 383 is connected through the conductor 33! to the capacitor SH of the impedance matching network consisting of capacitors 3H and 3'52 and resistor 31%. The capacitor 372 is connected to the bus 326, which is also connected to one side of the master power switch 366. The other side of the master power switch is connected to one terminal of the series-connected cathode heaters 388 and 3 i i and to the rectifier anode 328, the other terminal of the series-connected cathode heaters 388 and 354 being connected to the bus 326.

Thus the busses 33! and 32 are respectively connected by way of the coupling capacitors 31! and 312 to the terminals of the resistor 3'13, which in turn are connected to the line conductors of the home line 35! and to the respective wipers of the station selector switch the station selector switch 395 is of the conventional rotary type including two rotary wipers 88! and 382provided with individually associated contact banks. The contacts in the contact banks respectively associated with the rotary wipers 38l and 382 of the station selector switch 305 are paired and terminate the corresponding line conductors of the home lines extending to the other stations #2, etc. The impedance network including the coupling capacitors 3H and 3'12 and the resistor 373 matches the apparatus disposed at the station #1 to the home line 35! and to any of the home lines extending to the other stations #2, etc, selected by way of the associated station selector switch 365. More particularly, both the transducer 3il and the impedance network mentioned are adapted to be matched both to the input and to the output of the tetrode amplifier, as explained more fully hereinafter.

Similarly, the apparatus disposed at the station #2 comprises a transducer GU! operative selectively as a transmitting microphone and as a loud-speaking receiver; a combination rectifier and amplifier tube 3E2; a talk-listen key 593; a master switch ie for connecting the tube 632 to a source of volt A. C. power supply; an impedance matching network including a station selector switch 465; and a home signalling line t5l, accessible to the selector switches at each of the other stations.

Preferably, he transducer 35! is of any suitable type, such for example as the electrodynamic or the piezo-electric type; while the tube Q82 is of the 11'7P7GT type incorporating a rectifier portion (including an anode 496, a cathode 407, and a cathode heater 488) and a beam power tetrode portion (including an anode 499, a screen grid Me, a control grid 5H, a cathode H2, beam electrodes M3 and a cathode heater 456), In the tube 662, the tetrode portion constitutes a voltage amplifier when the transducer 40! is functioning as a microphone, and constitutes a beam power amplifier when the transducer 433i is functioning as a loud-speaking receiver, Also, in the tube 182 the rectifier and amplifier portions are enclosed in a common envelope 415; while the cathode heaters 663 and 414 are connected in series to the master switch 494.

The talk-listen key 393 is of the conventional two-blade double-throw type, selectively operative between talk and listen positions. Specifically, the talk-listen key 593 comprises two blades M6 and lii'i that are operative together and normall biased to the listen position.

Considering the connection and arrangement of the circuit network in greater detail, one terminal of the transducer Gill is connected to the blade Gil of the talk-listen key 493 and the other terminal of this transducer is connected through the bus 426 and the cathode resistor 429 and cathode resistor shunting capacitor 136, to the cathode 3 i 2 of the tetrode amplifier.

The make contact associated with the blade 6 l 6 and the break contact associated with the blade dil are connected through the impedance network (consisting of the resistor 36i, coupling capacitor M2 and grid leak resistor 453) to the control grid HI of the tetrode amplifier. The break contact of the blade MS and the make contact of the blade M7 are connected together and through a coupling capacitor ,64 to the anode 469 of the tetrode amplifier. The anode 489 of the tetrode amplifier is connected to the screen grid M0 of the tetrode amplifier through the resistor 655, which in turn is connected to the filter network consisting of the filter capacitors E24 and t2? and the filter resistor (#25. The filter resistor 325 and the filter capacitor 821 are connected to the cathode 40'! of the rectifier. The blade MB of the talk-listen key 403 is connected through the conductor 33i to the capacitor 4?! of the impedance matching network consisting of capacitors All and 412 and resistor 473. The capacitor 412 is connected to the bus 426, which is also connected to one side of the master power switch 404. The other side of the master power switch AM is connected to one terminal of the series-connected cathode heaters 483 and il l and to the rectifier anode 406, the other terminal of the series-connected cathode heaters 468 and 4M being connected to the bus 426 Thus the busses 43! and 426 are respectively connected by way of the Coupling capacitors All and 472 to the terminals of the resistor 413, which in turn are connected to the line conductors of the home line lEl and to the respective wipers of the station selector switch 405; the station selector switch 485 is of the conventional rotary type includin two rotary wipers 48! and 482 provided with individually associated contact banks. The contacts in the contact banks respectively associated with the rotar wipers Gill and 682 of the station selector switch 465 are paired and terminate the corresponding line conductors of the home lines extending to the other stations #1, etc. The impedance network including the coupling capacitors 4H and 412 and the resistor M3 matches the apparatus disposed at the station #2 to the home line 45! and to any of the home lines extending to the other stations #1, etc., selected by way of the associated station selector switch 695. More particularly, both the transducer 49! and the impedance network mentioned are adapted to be matched both to the input and to the output of the tetrode amplifier, as explained more fully hereinafter.

Considering now the operation of the intercommunicating system, when the person at the station #1 wishes to communicate with the person at any other station connected to the system, for example the person at the station #2, he first operates the talk-listen key 3&3 from its normal listening position to its operated talk position, as illustrated in Fig. 3. This operation of the talk-listen key 383 at the station #1 causes the transducer 39! to be operative as a transmitting microphone instead of as a loud-speaking receiver, and causes operation of the tetrode amplifier as a first-stage voltage amplifier instead of as a second-stage power amplifier. The person at the station #1 then operates the station selector switch 355 to the position corresponding to the desired station, such for example as to the second position, corresponding to the station #2.

It is further assumed that at this time the master switch 394 at the station #1 occupies its closed position and that the master switch at each of the other stations, such for example as the master switch 464! at the station #2, occupies its closed position, When the master switch 3% at the station #1 is closed, the source of 110-volt alternating current power supply is connected directly across the series-connected cathode heaters 308 and 354, whereby the heaters mentioned efiect heating of the associated cathodes 38'! and 3I2 in order to render these cathodes electron emissive. Also, closing the master switch 3115 applies the 1l0-volt alternating current to the anode 3535 of the rectifier. When the positive half-cycle of the alternating current is applied to this anode 3%, current flows between the oathode 323? and the anode 3%, thereby charging the capacitor 321; and at the same time some of this current flows through the resistor 325, also partially charging the capacitor 324. Also, the rectified current applies a positive potential to the screen grid SIB of the tetrode amplifier, and current flows thence through the resistor 355 to the anode 399 of the tetrode amplifier, thereby rendering the amplifier operative. When the negative half-cycle of the alternating current is applied to the anode 356 of the rectifier, no current flows between the cathode 30'! and the anode 3G6; and during this half-cycle current for the tetrode amplifier is supplied by the capacitors 324 and 32'! of the filter network, inasmuch as during this half-cycle these capacitors at least partially discharge, thereby applying a positive potential to the screen grid 3 l 0 and current through the resistor 365 to the anode 309 of the tetrode amplifier.

Inasmuch as the transducer 39! connected to the blade 31'! of the talk-listen key 303 is coupled by way of the capacitor 362 to the control grid 3 of the tetrode amplifier, modulated potentials produced by this transducer modulate the electron stream through the tetrode amplifier. The modulated currents in the output of the tetrode amplifier are impressed by way of the coupling capacitor 364, the blade 316 of the talk-listen key 3%, and the associated break contact, upon the conductor 33!. Thus the output of the tetrode amplifier is applied between the bus 326 and the conductor 33L which are connected to the capacitors 31! and 312 across the wipers 38] and 882 of the station selector switch 305 and consequently across the line conductors of the selected home line extending to the station #2. Accordingly, the transducer 3M is operative as a transmitting microphone to control the tetrode amplifier, whereby voltage amplified undulating signal currents are transmitted over the station selector switch 305 and the selected home line extending to the apparatus at the sta tion #2.

Considering now the operation of the apparatus at one of the stations operating as a receiving station, such for example as the station #2, the amplified undulating currents transmitted over the associated home line 45! are impressed across the resistor 413 and consequently by way of the coupling capacitors 4H and 412 across the bus 626 and the conductor 431. More particularly, the conductor 431 is connected by way of the blade 416 and the associated break contact of the talk-listen key 403, occupying its normal listen position, and the coupling capacitor 4'62 to the control grid 4! I of the tetrode amplifier, whereby the electron stream between the anode 489 and the cathode 4|2 of the tetrode amplifier is modulated in accordance with the received undulating currents. The output of the tetrode amplifier is applied from the anode 609 of the tetrode amplifier through the coupling capacitor 564 and the break contact of the blade M1 of the talk-listen key 403 to one terminal of the transducer 453 l now functioning as a loud-speaking receiver, the other terminal of the transducer dfil being connected to the bus 426. Thus, the transducer Ail] functions as a loud-speaking receiver to reproduce at the station #2 the signals received over the associated home line 45i from the station #1. Also, at this time at the station #2 the master switch 404 occupies its closed position, thereby rendering the rectifier operative in a manner identical to that previously explained in conjunction with the rectifier disposed at the station #1. Thus at this time the transducer 40! functions as a loud-speaking receiver, and the tetrode amplifier functions as a beam power amplifier.

Of course it will be understood that in the intercommunicating system, after the person at the station #1 is through talking he may restore the associated talk-listen key 303 to its normal listen position, whereby the station #1 is converted to a receiving station; and at this time the person at the station #2 may operate the associated talk-listen key 403 to its talk position, whereby the station #2 is converted to a transmitting station. Further it will be understood that when any one of the stations is operating as a transmitting station, the associated transducer functions as a transmitting microphone and the associated tetrode amplifier functions as a voltage amplifier; whereas when ony one of the stations is operating as a receiving station, the associated transducer functions as a loud-speaking receiver and the associated tetrode amplifier functions as a beam power amplifier.

Finally, it will be appreciated that only one station at any one time may operate as a transmitting station, whereas normally only one station operates therewith as a receiving station. However, a conference connection can be set up between the transmitting station and any number of receiving stations. This is accomplished by the person at the transmitting station making successive calls to the persons at the receiving stations and causing the persons at the different receiving stations to operate their associated station selector switches in order to select the home line extending to the transmitting station. When a conference connection is thus set up, the station selector switch at the transmitting station may be released in view of the fact that the home line extending to the transmitting station has been selected by the station selector switches at the connected receiving stations.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that many modifications may be made therein and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. An intercommunicating system comprising first and second stations and a signalling channel extending therebetween; each of said stations including a transducer operative selectively as a transmitting microphone and as a loud-speaking receiver, an amplifier provided with input and output terminals, a switching device selectively operative between talking and listening ositions, and a circuit network so connected and arranged that said first station switching device is operative when in its talking position to connect said first station transducer to the input terminals of said first station amplifier and to connect the output terminals of said first station amplifier to said signalling channel, and that said second station switching device is operative when in its listening position to connect said second station transducer to the output terminals of said second station amplifier and to connect the input terminals of said second station amplifier to said signalling channel at the same time as said first station amplifier is connected to said signalling channel.

2. An intercommunicating system comprising first and second stations and a signalling channel extending therebetween; each of said stations including a transducer operative selectively as a transmitting microphone and as a loud-speaking receiver, a vacuum tube provided with input and output terminals, a switching device selectively operative between talking and listening positions, and a circuit network so connected and arranged that said first station switching device is operative when in its talking position to connect said first station transducer to the input terminals of said first station vacuum tube and to connect the output terminals of said first station vacuum tube to said signalling channel, and that said second station switching device is operative when in its listening position to connect said second station transducer to the output terminals of said second station vacuum tube and to connect the input terminals of said second station vacuum tube to said signalling channel at the same time as said first station vacuum tube is connected to said si nalling channel.

3. An intercommunicating system comprising first and second stations and a signalling hannel extending therebetween; each of said stations including a transducer operative selectively as a transmitting microphone and as a loud-speaking receiver, a vacuum tube of the beam-power type provided with input and output terminals, a switching device selectively operative between talking and listening positions, and a circuit network so connected and arranged that said first station switching device is operative when in its talking position to connect said first station transducer to the input terminals of said first station Vacuum tube and to connect the output terminals of said first station vacuum tube to said signalling channel, and that said second station switching device is operative when in its listening position to connect said second station transducer to the output terminals of said second station vacuum tube and to connect the input terminals of said second station vacuum tube to said signalling channel at the same time as said first station vacuum tube is connected to said signalling channel.

4. An intercommunicating system comprising first and second stations and a signalling channel extending therebetween; each of said stations includin a transducer operative selectively as a transmitting microphone and as a loud-speaking receiver, an amplifier of the pentode type, a rectifier connected to rectif alternating current for supplying said pentode with direct current, a high capacity filter circuit for filtering the rectified output of said rectifier; a separate alternating current supply connected to each of said rectifiers; an impedance network for said first station for matching the input and output of said first station amplifier to said first station transducer and signalling channel, respectively; an impedance network for said second station for matching the input and output of said second station amplifier to said signalling channel and to said second station transducer, respectively; and means for simultaneously connecting said amplifiers to said signalling channel.

5. An intercommunicating system comprising first and second stations and a signalling channel extending therebetween; each of said stations including a transducer operative selectively as a transmitting microphone and as a loud-speaking receiver, an amplifier of the pentode type, a rectifier connected to rectify alternating current for supplying said pentode with direct current, a high capacity filter circuit for filtering the rectified output of said rectifier, a talk-listen switch for connecting said transducer either to the input or the output of said pentode amplifier; a separate alternating current supply connected to each of said rectifiers; an impedance network for said first station for matchin the input and output of said first station amplifier to said first station transducer and signalling channel, respectively; and an impedance network for said second station for matching the input and output of said second station amplifier to said signalling channel and to said second station transducer, respectively; said amplifiers being connected simultaneously to said signalling channel.

6. An intercommunicating system comprising a plurality of stations and a signalling channel extending therebetween; each of said stations including a transducer operative selectively as a transmitting microphone and as a loud-speaking receiver, and an amplifier having at least a pair of stages; one of said stages being at each of said plurality of stations, each of said stages being adapted to function either as an input stage or as an output stage; impedance networks connected to each end of said signalling channel, said impedance networks and said signalling channel being connected between and simultaneously to the stages of said amplifier.

7. An intercommunicating system comprising a plurality of stations and a signalling channel extending therebetween; each of said stations including a transducer operative selectively as a transmitting microphone and as a loud-speaking receiver, and an amplifier having at least a pair of stages; one of said stages being at each of said plurality of stations, each of said stages being adapted to function either as an input stage or as an output stage; impedance networks connected to each end of said signalling channel, said impedance networks and said signalling channel being connected between the stages of said amplifier; and means at each station for connecting the stage at that station to function either as an input stage or as an output stage.

8. An intercommunicating system comprising a plurality of stations and a signalling channel extending therebetween; each of said stations including a transducer operative selectively as a transmitting microphone and as a loud-speaking receiver, and an amplifier having at least a pair of stages; one of said stages being at each of said plurality of stations, each of said stages being adapted to function either as an input stage or as an output stage; impedance networks connected to each end of said signalling channel, said impedance networks and said signalling channel being connected between the stages of said amplifier; and means including a ta1klisten switch at each station for connecting the stage at that station to function either as an input stage or as an output stage.

9. An intercommunicating system comprising first and second stations and a signalling channel extending therebetween; said first station including a microphone, a first-stage amplifier provided with input and output terminals, and means including a circuit network for coupling said microphone to the input terminals of said first-stage amplifier and for coupling the output terminals of said first-stage amplifier to said signalling channel; said second station including a, loud-speaking receiver, a second-stage amplifier provided with input and output terminals, and means including a circuit network for coupling said loud-speaking receiver to the output terminals of said second-stage amplifier and for coupling the input terminals of said second-stage amplifier to said signalling channel.

10. An intercommunicating system comprising first and second stations and a signalling channel extending therebetween; said first station including a microphone, a voltage amplifier provided with input and output terminals, and means including a circuit network for coupling said microphone to the input terminals of said voltage amplifier and for coupling the output terminals of said voltage amplifier to said signalling channel; said second station including a loud-speaking receiver, a power amplifier provided with input and output terminals, and means including a circuit network for coupling said loud-speaking receiver to the output terminals of said power amplifier and for coupling the input terminals of said power amplifier to said signalling channel.

11. An intercommunicating system comprising a first station including a microphone, a second station including a loud-speaking receiver, and a link interconnecting said microphone and said loud-speaking receiver; said link including a first-stage amplifier provided with input terminals coupled to said microphone and output terminals, a second-stage amplifier provided with output terminals coupled to said loud-speaking receiver and input terminals, and a signal line extending between said first and second stations, one end of said signal line being coupled to the output terminals of said first-stage amplifier and the other end of said signal line being coupled simultaneously to the input terminals of said second-stage amplifier.

12. An intercommunicating system comprising a plurality of stations and a plurality of signalling lines respectively extending to said stations; each of said stations including a transducer operative selectively as a transmitting microphone and as a loud-speaking receiver, an amplifier provided with input and output terminals, a selector switch having access to the signal lines extending to each of the other of said stations, a switching device selectively operative between talking and listening positions, and a circuit network so connected and arranged that said switching device is operative to its talking position to couple said transducer to the input terminals of said amplifier and to couple the output terminals of said amplifier to said selector switch and to the associated signalling line and that said switching device is operative to its listening position to couple said transducer to the output terminals of said amplifier and to couple the input terminals of said amplifier to said selector switch and to the associated signalling line.

WILLARD FELDSCHER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,954,195 Black Apr. 10, 1934 1,982,068 Parker Nov. 27, 1934 2,087,027 Glaser July 13, 1937 2,146,362 Thomson Feb. 7, 1939 2,269,144 Campbell Jan. 6, 1942