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4C27012 . .. .. _. Telephone antral .- ... 1 • 1 • TG-12. 4A2788. _ . ..... Tflegrapb ocnhai ,,,," ... ------ --- --- 1 1

T G-3 (teletypewriter),

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6QIOOL • • ••• _. A~lo LG-L __________ __ ______ 1 1 1 I 6HT.l7 ( )----- Ado RL-21- (

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Bla.ekout Ught (note 1) __ ____ __ _ 2 2 2 • 181445 __ _____ _ c.,. .... embly CC-345, 100 • , • , ft. Ion, (5 pr.). 181«11 ________ CabM _mblr Co-MS, " mile 2 3 , • 10Dg (5 pr.). 18IHL _______ Cable stub CG-344, 10 ft. 10"" , 10 , 10

(Ii pr.) . 6F705 __ ____ ___ _ Chest 80-6 __ ____ ___ _________ 2 3 , 3 6ZAOO2A.I ______ Flasblight TL-In--A ___ ______ _ 3 3 • • GZA810 __ __ • __ ._ Glovell Lo-to, pr ______________ • 3 • 3 6H2504 ________ Reel DR.-t .......... _. ___ •••• 2 2 2 2 6H2505 • •• • ••• _ lli>el DR- IL ____ ______________ ------ --- ------ --- 1 6H2.501 ____ ____ ReeIDR- ' ______ __ ___________ 2 • 2 • 6H6231 __ ____ __ Reel unit RL-31. ____ ____ _____ 1 1 1 1

Sign [note 2) ________ ___ _______ 1 1 1 1 4B5CXl8A _______ Telllpbone E&-8-A ___ ___ ___ ___

" .. " .. 4E9304 __ ______ Tenninal8~.ip TM- IM _______ _ 3 • • • 181 10B ______ __ Wire W- II(}.8, mllea _________ • 1 1 1 , e XPE NOABLE 1"~ .. 8

SA30 __ ________ Battery BA- 30 __________ ____ __ 80 .. .. .. Camouflage material {lJIandard

."'. ehiekeD wi"" cW.}. Los book ___ _______ __ __ _____ __ 1 1 I I

6Z698t __ ____ ___ Marline RP- 2, poUDde _________ ------ -- -- -- 1 1 6Z7904 _____ ___ _ Rop" RP- I , be.ll . ____ _________ 20 20 20 20 IAI6 __ ~ _______ Seiling "'ire W- 16, 81'001. __ ___ 100 100 100 100 4Z7272 _______ __ TaglI Me-72. _______ ____ _____ _ 100 100 100 100 6N8594 ________ Tap", rubber, TL-H, rolho ______ , , , , 6~85S3 ____ ____ Tape, friction, TL-83, ro1lll. __ __ , , , ,

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c, When the O-trucks, 2lh-ton, cargo, are used, the following tele-graph equipment may be carried in the O-trailer, I-ton, 2-wheel, cargo, att,a()hed to the firet eehl'lon truck wht'n a movement of the command poat Is being made:

2 Wetypewriter sets EE-97- A. 2 telegraph sets TG--lI--A,

tl.. The ruggested loading plans ILre shown liS folloW81

:r"No. t.o.d .... plu .,....:.

18 ~overoent_ . __ • __ • __ •• _. ____________________ __ __

19 ~ratlon ___ . _. _______________________ ________ __

20 o¥tUleDt_ •• _____ __ ••.. ________________ . ______ _

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u_ o·truel<

IJ'-ton, carso, Do.

2J'-toD, Do.

C",",O.

Tho loading plan is the aame for each of the th~ trucks of II com-pany, ezoopt that in the case of a rear echelon truck, a reduced amount of equipmt'nt is carried In accordance with the table in b above.

~, Three chest.

TM: 11:...336 C 1 TECHNICAL MAN-UAL

(1) For n tremel!l critical ,ituationa, blackout lights should be in-stalled. Turn these lights off whenever entrance and exit of per-sonnel is taking place. Use the improvised curtain shown in figure 22, and the end curtain of the truck. Ventilation at night is by meall,l of natural convection of air currents through the openings between the canopy and end curtain.

(2) For 11QTfi'I.Ill rutrictWnr, entrance and e:.:it of personnel from the truck usually is permissible with the blackout light turned on, pro-

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vided the improvised curtain shown in figure 22 is used to seal the opening into the truck from direct view. In this case, the end cUI'tain of the truck need not be used, Incrnsed ventilation may be obtained by propping up the CIUlvas CAnopy by means of short sticks and retying the ropes to pre\'ent accidental lifting of the canvas by the wind,

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TM 11-336 c , TECHNICAL MANUAL

(3) Where no enemy ground troops would be likely I() observe Ille p re!>ence () I the mobile telephone central ofJk'6, and where !i0Curity RJ,'1linst observati()n by enemy aircraft only is required, the mobile telephone central ()ffioe may be operated without the end curtain

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or the impro\-ised entrance cn rh iu iu plare_ It is n.,.,;ulllC\1 tlill t. l ila blackout lamp used will pro\- ide an intensi t.\" of ilhUll inutiun so low that the dir'ect ray of the "HUP will not be vibiLle li t II. distalR't' uf IlP-

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proltilllll. t.ely 1,000 feet. Under this condition, II.ny refl ected light will be unobservable Itt II. milch shorter distance Ilnd adt'(ltlll.te secu rity will be maintained.

IA. G. 062.11 (4_1r.-t3).] (e I , lr"-J 12. 1943. )

By ORDER OF THE SECRETMIY OF 'VAR:

OnICIAL:

J. A. ULlO, Major General,

G. C. MAR":;HALL. Oh:l'/ of :Staff,

TM Adjutant Gerural.

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TELEPHON"'E~CENTRAL OFFICE SET TC-12

WAR DEPABTMENT, C>u>

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TM 11-336 o •

TELEPHONE CENTRAL OFFICE SET TC-12

cu.NOEsl WAR DEPARTMENT, : No.8 WABBIli/nTON 25, D. C., 25 AugU8t 1944.

TM 11- 336, 18 JanuRry 1043, is changed as follows: 1. Purpose.- Telephone central office • • • in paragraph 2.

COMPONENT PARTS

A_' Q""". A" 5o'" APf'I'Ol lmo. .. , blpf/Ulr ,I .. (1110"-) -~. IIIJ ... C hl ("",,0HlZ2, __________ .• _ Sy.:II. 6Yo x 6~.--. -- _ . .. ___ , S",ltehboard BD--91 ~ ___ . __ -.- -1 171!t (18% ,,2&*/1, .. ____ • '" Total weight approxlmately ... _ ___ ~ . __ __ •.. __ __ ._. _______ m I

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TELEPHON E CENTRAL OFFICE SET To-l2

Figure:2 is r{'S("indcd lind the following is substitutell therefor:

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4. Setting up and connecting equipment.

• • • • • • • m. P lug II headset HS-3O-(&) and chest set TD- l into the jllck

JK--37 mounted ill the fron t or the key shelf. Two b(!lldsets HS- 30-(& ) and ehest sets TD- l are normally carried in t he compartments provided in the fron t cover.

7. Magneto line circuit (fig. 5).

• • • • • • • c. M agneto line circui ts in switchboards BD- 14, DD-71 , BD- 72,

BD- SO, BD---S9, BD- 91, BD- 96, BD- 110, and in commercio.l swik h· boards .

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TM 11-338 03

TELEPHONE CENTRAL OFFICE SET TC-t2

d. Line circuits equipped • "' "' in commercial switchboardB .

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23-C COMBINED ,JACK ANO SIGNAL

TL usa Flouu Id.-Magneto line circuit equipped ror ulesrapb.

• • • • • • • 7.1. (Added.) Megneto line circuit equipped for telegraph (fig.

5.1).-Line circuits 0, I , 2, and.3 operate fill covered in paragraph 7, ex-u pt that r inging and ta.1king take place through repeating coil 0-288. Telegraph circuits connected to the telegrB.ph 9inding poate operB.te without int-e rlerenu with the talking circuit if the two line wires are of equB.l resistB.nce. Current enwing the line B.t the telegraph binding post divides B.t tenninai 2 of the repeating coil; bB.if of the current

1 flows through the 2- 3 winding B.nd the tip side of the line, the other hB.lf flOWB through the 2- 1 winding and the ring side of the line. The 1- 2 and 2- 3 windings are iden tical. With equal currents flowing in oppoaite directions through these windings, the magnetic fields 0PPOBe each other and the voltage induced in the talking circuit (4--5 winding) is zero. At the opposite end of the line, the action is t·he Baine, except thB.t the current flow will be from the line to the tt>lcgraph leg.

11. Operator'. telephone circuit (fig. 9).- An antisidetone tele-phone • • • grouping cord CD-611. H eadset HS-80-(&) Illld chest set TD- l may be connected to the operator's telephune circuit

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TELEPHONE CENTRAL OFFICE SET TO-12

by means of II. plug PL-58 and the js.ek JK- 371ocatOO on tbe left front of the key shelf . . Figurt' 12 is r('8(linded and the follo~ing is substituted therefor:

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--FlOun 12.-S,,·j t chboard BO- 91- muter Ichern.tic diagram-CoDt i oued.

17. (Supersedod.) Preventive maintenance.- a. General.- The greatest single facwr in trouble-free operation is careful bandling

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TM 11-386 o.

TELEPHONE CENTRAL OFFICE SET TO-I3

of the equipment while packing and unpacking, transporting, and installing. Much potential trouble can be eliminated by routine checks. The frequency of the routine cheeks depends on the number of calls bandled and the USfLgll of the equipment.

b. Imputitm and u,l!.-The following will serve as a guide to the inspections and lesls to be made upon iostallation and for routine checks:

(1) Set up'switclIooard BD-91 in an operating position (par, 4). (2) Inspect aU sectioos of the switchboard for damaged or mis.iing

pam, giving particular attention to corda, plugs, keys, drops, oper-ator's telephone equipment, and band generator. While inspecting the cords milks SIll'6 they are of the proper length and that th e weights hang evenly.

(3) Connect one terminal of 8 test telephone EE-8 to the GRD terminal on thllswitchboard BD-91 , and touch a wire from the other phone terminal to each line terminal binding post of the panel. Then ring from the test telephone. If the line is grounded , the generator will turn hard. Usually grounds ooourring in the protector panel are caused by dirty or improperly moun.ted protector blocks.

(4) With the teet telephone across each pair of line terminals at tbe protector panel at the rear of the switchboard, ring from the telephone on each pair in turn . The shutter should fall and the night alann should ring.

(S) At! llach shutter is rung down , plug into the line jack of that line with one of the cords, thus restoring the shutter. Throw the listening key and talk to the man who is at the test phone.

(6) Ring the test phone by operating the appropriate key and turning the switchboard generator crank. In the course of these ringing and talking tests, use each cord of each cord circuit at least once, so as to test both sides of every cord circuit.

(7) Cause the test phone to ring on each cord to test the super-visory drops of the cord circuit.

c. Cleaning plug8.-To maintain high grade transmiMion through the cord circuits, all plugs should be cleaned as often as required to maintain brightness. Use polish, metal, paste (stock number 6G 1516) , or equal, for polishing the switchboard plugs. Take care to remove thoroughly all surplus polishing material.

d. Cleaning contac~ and jaeb.- ( l ) When it becomeA necessary to clean the contacts of keys, drops, jacks, etc., burnish them with a burnishing tool, or its equivalent. The contact burnisher furnished

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TM 11- 336 C 3

with the telegraph set TG-5-A, or tool, switchboard, contact burnisher (stock number 6R4 1 0658), a part of telephone electrician's tool equip. ment TE-49 (stock number 6H38049) may be used. To burn ish, normally open contacts of keys, jacks, drops, etc., place tho blade of the burnisher between the contacts and press them together or operate apparatus manually to get a slight pressure against tho burnishl'r blade. 1\'Iove the blade back and forth betweon th!) contacts. Repoat this process two or three times for the best results. I II the case of normally closed contacts, the tellsion of the sprinb'1l themselves usuII.II .\· will give sufficient pressure against the burnisher. " 'hen it is im· possible to properly clean the contacts by ordinary burnishing, clea n and flush tho contacts by dipping ~he !lat end of It toothpick into n .::leaning fl uid, such as carbon te trachloride, solvent, dry cleaning, or a similar solvent, awl place the fluid on the contacts (held slightly apart) without rubbing. Repeat this process to flush ofT the dirt. Then burnish the eontacts. Do not permit the fluid to com!) in con· tac t with insulators, spoolheads, etc.

(2) T o clean tho tripping latch, top notches of the shutt er, and the shutter.hinge plate of the drops and signals (figs. IS.I and 15.2), saturate a clean cloth or brush with carbon te trachloride or solvcnt, dry cleaning, and npply to the parts to be clclllied. Then wi pe the parts dry with a cI ('IUl cloth.

MOUNTING 'C'", ___ , SHUTTEII HINGE HINGE PLATE TIIIPPING

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FIGURe 15. 1.- o.,s lgnllt ion or part.. or a 5611 drop

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Fill!}R" If>,Z,- Oe!ignation of t",r\.8 of .. 2aC oomb;ned jack and sign .. 1 R"d ... 34C .upcrv;80ty ~ ign.1.

17.1. (Added .) Moistureproofing and fungip rooflng.- a . G~n. ~ra/.--.communictlt ion l fl.i lures COllllllonly occur when Signal Corps equipment is opcrllted inlropicai areas where temperature and relative humidity are e.drcmcly h igh. Tho following problellls are typical:

(I ) R esistors find cfl pacitol1:l fa il. (2) E lectrolyt ic action takes place in coil!!, cilokf:!:l , transformer

windillb'1i, etc., causing cvcntunl break-down. (3) Hook-up wire Illld cnhlf' insulation brcak-

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TELEPHONE CENTRAL OFFICE SET TC- 12

T.M U~38 c.

relay contaet8, open switcbes; air capaeitoI1l, BOCketa, bearings, etc., a.re covered witb masking tape.

(4) Equipment is thoroughly dried by beat to expel moisture which tbe circuit elemf'nts bave absorbed.

(5) All circuit elementl and all parts of tbe equipment afe 8prayed or painted witb three coati of moistureproofing and fungiproofing varnish . . (6) The equipment is given a final operational cbeck.

c. SUp-IYg-8Up instructiom.- (I ) Di&a.!nm6ly.- (a) Open rear door of switchboard by looserun'g two knurled screws. This will expose one side of the protector panel.

(6) Loosen latches on left edge of panel and open protector pil,nel, exposing rear side.

(c) Raise panel at top of switchboard . (d ) Release lo\\'er panel and remove cords from tbe cord shelf. (e) Remove four screws from front of each combined jack and drop

mounting plste. Pull unitl forward until terniinals Sfe exposed. (j) Open tbe large portion of the locsl cable running up tbe side of

tbe fram e to the rear panel. (g) 1.oo8('n screw at right end of keysbelf. Open k{'.yshelf and

loosen screws bolding tbe keys in placc. Tum tbe clamp pi{'ces so they will slide througb the key mounting bars.

(h) On tbe right fron t of the plug shelf, remove the t ... ·o screws bolding a small section of phenolic plate . Lift out piau>.

(i) Remove tbe two screws supporting the rear of the band gen-erator. Open keyshelf and remove two screws bolding front ' of gencrator. Remove generator and disconnect the connected leads.

(2) Ma8king.- (a) Mask fuse connecting clip springs, carbon blocks, binding posta TM- 198 snd TM- 85, and grouping and power plug receptacles located on protector panel.

(6) Mask dial-mounting opening on under side of top compartment. (e) Mask cord u>rminal end of cord fasteneI1l snd buzzer. (d) Place shield under supervisory drops. (t) Mask the wire connecting screws snd contact pointe. of tbe

spring pile-up on the generator. (3) Drying.- Dry all parts for 2 or 3 hours at 1600 F.

, (4) Varoi.!hing.- Apply three coats of moistureproofing and fungi. proofing varnisb ·according to the· following instructions: . .

(a) Spray both sides of protector panel. (6) Spray top compartment, including repeating coils.

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TJlll-338 c.

TELEPHONE CENTRAL OFFICE SET TC- 12

(e) Spray cord shelf, capacitor mounting plate, and local cable 011 the under side of cord shelf.

(d) Use brush to apply varnish to the spring pile-ups of jacks, soldered connections, and ends of wire ilUlulation in lower panel.

(e) While combined jacks and drops are drawn forward, spray the under side of the top compartment where the leads to the repeating' coils are exposed.

(/) Spray the opt-ned-up portion of the local cable running ,up tile side of the frame to the rear panel.

(g) Brush varnish on the cable forms and individual conductors from the main cable form to the soldered jack and drop connections.

(.4) Close the keyshelf and lift out the keys one at a time. Brush varniah on the spring pile-ups~ the soldered connections, and on the insulation of the connected wiree.

(\) Brush varnish on the local cable form and the conductors to the keys, gent'rator, and opt>rator's jacks. Do not varnish terminal ends of generator leads.

W Use brush to varnish spring pile-up 00 generator. (1:) Turn generator upside down and brush varnish on the coil

winding of the armature. Revolve the armature and varnish the other side of the coil.

(6 ) R~Bem6lin!1 and testing.- (a) After varnish is dey, remove all masking . . (b) Cheek all contacts for traces of varnish and, if necessary, eIl'all with varnish remover, and burnish.

(e) ReeMemble and drew cabling. If varnish is broken during Ihis operation, touch up with varnillh.

(5) Replace the combined jack and drop mounting strip . . (~) Replace the keys in the keyshelf. (j) Replace generator in switchboard. lq) Test switchboard for proper operation in tl.ttordance with para-

graph 17b. (Il) Mark MFP and date of treatment: This marking should be

stencillt>d near the nameplate. d. RrjeTtnce.- For a full dcscription of the varnish spray method .

of moistureproofing and fungiproofing, refer to TB SIG 13. 17.2. (Added. ) Trouble location testlll.- The following tahle pro-

vides a testing sequ('llce for isolating swilc.hboard t.roubles:

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2. Tellti"g hand.ring;"I1_''''!_ erato. from • ."itch_ board througb any or all cord cireuil.l!.

b. Signaling tut

1. Test ing line and trullk ~ignab throuRh line pro~n &lid fWlell .

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'"-a. Testin!! tom circuit .uper-

"wry BiIl".IB.

c. TroMmi.,wn lUI

I. TCllt;", open"',o.', tcLe-phone, eord, line, and tMlnk eirc:ultlo, ,,'heu bat--lery ."1'1'1,. i. derived frol11 loclII dry cell._

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Same U lelt I, ueep~ jn_ llert rortl-cireuit plU!! in Un. or trunk jack.

I "!left operator'. telf,phone-llel p lUM; In jack and ,,,,.en. oord_dreuiteord in line Or t .unk jack: rinll& "earby .. ,.Uon or tl.'At Mlt; o pe r. ate talk!",; hy IlIId talk betwc'" e fllWr.

I ."" ...... 2 A. S~a1 operateo •• _____ _ 2B. Signal (lotto \0 open.te._

3A. Coni Bupen ·oory BiK',a1 (Aill to operate, ~ ...... tor handle t urna Ul!ily.

3B. Coni ouper\';lIOry ,illnal r.i1.o to operate. ~n'"'"'tor handle t unl' hard.

1 A . Operator hears .tation, but atatlon doe. not hear operato r.

I B. Stat ion hcarl operator hu t operator d~ not hear "talloI'.

IC. & t h stat iOIl and oper-. tor unab", to ht.ar .....,h otht:r .

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Blown fUM:. Broken Or unlOldered local c.b .... lead

lot Jtoek drop Or protector, diny ja.et o r defective drol), Check ! (If open In toeal able.

Opooorate . 110,&1 m."ual iy \0 check ""e.,hani.,.. operation - ...... ke adju ...... """,,18 j( I"I!

Check poIi tion or gronp!nl key (ahmud be OFfl . U !nd!e&Uon 18 nUl t he same. proc !ed .nt h tal l A a nd I R.

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18. Packing for Army transportation .

• • • • • • • b. Place the ringing • • • of the cl amp. Place headseta

BB-30- (&) and chest sets TD-l in the proper compllrtments in the front cover. Adjus t the designation • • • supervisory drop shutters.

• • • • • • • 19. List of replaceable parta.--a. TelephlYTU untral office set I

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TM 11-336 TELEPHONE CENTRAL Ot' n CE SET TC- 12 C 3

c. (SUPCrsClJed.) GM8t 8tl TD-I.

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T-26 induding tbe follo"'ing It.cms: ST-Z4. ST-Z ..... SW-I I8.

CC-333, 6 ft. , 3-oonductor. PL--SS.

d. Headset BS-30-(&).

----'-""-"--I-~ ~I I' •• u... -

2 B7S0 __ .. _ . .. lIeadband ________ lIB-SO. 2 B2030 (& ) _ _ _ lleeeh n . _ .. ___ . . ll -SO-(&). 2 :11 620(&) •• _ Cord __ __ ._ •• ___ • CD-620-(& ) 2.eonduetor. 2 BI SOO. -. __ .. Inaen. __ . _. ___ __ JIIl-SOO.

e. Head and tAut 8tl HS-19. • • • • • •

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tIle' following chart is used with , but is not a po.rt of, telephone central officc set TC- 12.

Bloek No. --.~-:

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6GHiI6 .• -. . . _. Poli~h, metal, pa.>Jte. __ ___ __ . _. __ _ • _____ 2-

TM 11-336 C 3 TELEPHONE CENTRAL OFFICE SET To- I2

20. List of manufacturers and their addresses.

• • • • • • • • W. E. Co .. _ .... _._ W"",tern Eleetric Co ...... . Kearny, N. J .

Philadelphia, 1' •. B.. H . B. In". , __ . __ BUl h H . Eb:r, In,, ____ ... _ Stanley ______ .. _ .. Stanl.,. Worb .•... _____ _ N •• Brlt..ln, Conn.

1.0 . O. 'I(lO.T 0' ! nl M). I

By ORDER OF TilE SECRET ARY or WAR:

OFPICIAL:

O. C. MARSHALL, Ohief oj Staff

J. A. ULIO, Major Gemrai ,

Tht Adjutant G~ral.

DISTRIBUTION:

••

All prescribed In paragraph 9a, FM 21---£: Armies (10): Corps (10) ; Sv C (10) ; Dept (10) ; Def Comd (2) ; D (2);

I Bn 1 (3); IC II (4) ; Tech Sv (2) ; Arm & Sv Board (2); I Bn 1 (3) ; T /O « E 1- 27 , 1- 37, 1-47, 1-{l7 , i - Il7 , 1-127,

1- 130-1, 1- 137 , 1- 147, 1- 167,1- 252 , 1- 267, 1- 2778, 1-317, 1-4878, 1- 547, 1- 637, 1- 757, 1- 758, 1- 759, \ - 767, i -76S, 1- 7778,1- 779,1- 1027;

IC 11 (4) iT/O&E 11-885, 11- 247,11- 18, 11-47, 11-517S, 1I- 237, • 11-97, 11- 267 , 11- 217, 11- 107 , 11- 127, 11- 77, 11- 257, 11 - 287, 11- 5378, 11 - 557.

For explanation of symbols, see FM 21-6 .

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TM: 11-336 ,

TECHNICAl. MANVAI.) No. 11-&'16

WAR DEPARTMENT. W .UHllfOroN. January ]8, 1&48.

TELEPHONE CENTRAL OFFICE SET TC-12

SI!X:TlON I. General. Pa ... c.ph Purpose__ ___ ___ __ _______ _ ____ _ ___ _ _ ___ _ ___ __ 1 Descriptioll ___________ __ ____________________ _

n . Employment. Equipment lay-ouL ____ _____________ ___ _____ _

Setting up and connecting equipmenL ___ ____ _ _ Switchboard operation _________________ __ ___ _

III. Functioning of parts. Switchboa.rd ________ _______ ________________ _ _

Magneto line cireuiL ____________ . ___________ _

Trunk cireu it, did Hnd common battery manual. ( ' d . . .or elreu It, ___ __________ • __ __ ____ _____ ___ __ _

2

3 , , • 7 8 9

RiJlging circuiL ___________________________ __ HJ Operator's telephone circuit. _____________ ____ 11 Night alarm circuiL _________ .. _____ _______ ___ 12 Confllr",nce circuit ___ _________ ___ __ ___ ____ ___ la

Master I'IChemalit- and wiring iliagrams__ _____ _ _ 14 Main distributing fram"' _____ __ __ _____ ____ __ __ 15 Ringing equipment __ __ __ ___ ___ __ ________ __ __ 16

IV. l\hintilnan('e. ONleraL ____ ________ ___ ____ _________ _____ _ _ _ 17

Packing for Army transportation __ ___________ 18 V . .:supplemenlRrY dahl.

List of replaceable pali s_ _____ __ _____ _____ ____ 19 List of ma.nufnctureJ'S and their addl'llsHe8_ ___ __ 20

SECTION I

GENERAL P,," K'.P~

I>u~.e ___ __ _____ ____________ ____ __ __________ ___ ____________ __ ________ 1 J)eeeription _____ _______ __ ____ __________________ ._____ _____ ____ ____ ____ _ 2

1. Purpo8t1.-Telephone central office set T C-12 is for use at. Arm)' Air F orees squadron headquarters and at other headquaru-n1 which nlquire one or more telephone switchboards of t.he CIlpacity described in paragraph 2.

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UNIVtl1'im Of UlJfORNlA

.-. SIGNAL CORPS Appro>!·

QU&IIU" .- A M"".Im",. o.hlrplna- mOU unl, 01 .. (1_ " !eM (fIOWldo)

--- . -• Battery BA-23 (2 In tille, 2 spare) ___ ____ 2}; diameter ~ ,". 2 " &tU!ry BA- 30 (6 in !lOW, II ~p .. re) -- ___ __ 2Y. ~

IX _______ ___ Y.

• Cord CD-4S2 (10ft 10ng) • • ____________ ---------------- -- 2 • Cord CG--ZSS (50 rt long) ______ ___ __ ___ ------.- .... ------ " , Ground rod GP-29 __ __ ____ •• __ _______ _ 36100(1: I I" dit.m- " et.er. 2 H.od and ehellt !let H8-19. __ ___ _______ --- -_ . __ .. __ ._--_ . 2 , Maintenance equipment ME-30 '0 ,- IllY." 12Y. X 6. ____ " C8-18. , (:Qn"erter M - 2Z2. ______ • ________ • ___ _ Sy." 6,:" 6%. __ __ "" , Swlt

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, fu r nish ri ngi IIg cUlTo:nt when I IO-volt , OO-cycle II-C po wer is 1\ n l i1abl{l, u n!! C{)1werter M- 222, II blittery.operll l ~'(1 ringing '-'{Inverter , is pro-vi ded fo r elller'geney U>IIl . Elich gwilchbollrd t'()ll t lti n s the following:

1 operator 's posit ion. 1 operator 's telephone ci n;uit wi th grouping key. S t"ON circuits. • 1 ringing circuit . 20 line cil"'Cuits, mugneto. 4 lI'uuk circuits, commun buttery, Illlllluni lind dial. 1 dial rord circuit. 1 con ference circuit (4 jacks) . I night lilaI'm circuit.

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T he over-all size of swi tchboard BD-91 whell prepared for transpor. tation is Ii]!., by 180/.1 inches by 250/16 inches high. I n the operati ng posit ion, the height of the ~w itchbourd is 4.7%6 inches. The Ilpproxi.

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OOgtr •• 1 If"", UNIVE~\lTY Of CAliFORN IA

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Sl(lNAL COR P!;

lIlute weight is 2.15 pounds. The swilchbouro is KrI'llnged to be packed with in the ll.ngle iron hasc, so that a !!ep llntt8 packing case i8 Ilot nllCessory for Army t l'unsportlltion.

SI!:CTlON n

BM PLOYMENT

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PoroB'.ph EquIpment lay-out __ :~ ___ _ . __ __ ____ __ ____ _____ ____ __ _____________ ___ ____ 3

SeIling up lind CQnnecting eQul])ln.,"t__ ______ ______ ___ ___ ___ ___ __________ 4 Switchboard QPeratiOl' _______ _______ _______ _______________ ________ ______ • Ii •

3. Equipment lay,ou,t .-Beforo stnr ting lilly installation, the general disposition of the equipment should be decided upon with a view to local condi tions.

4. Setting up and connecting equipment.--a. Tum the lingle iron frllmework conta ining the swi tchboard to an upside down po!ii. t ion . Remove the seat top Ilnd draw out the extension legs of the

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TELEPaONE CENTRAL OFFICE SET TC- 12 • b. Turn the base to ease the switchboard outward upon the

ground, and lift the base upwaril. Place the base in the desired operating location. Set the switchboard on the bllse making sure that the dowels on the switchboord fit into the holes in the top of the base.

c. Unfasten the cord compartment on the bottom of the switch-board and let the cords and weights drop into position. 'Clamp the switchboard to the base by means of the two wing nut bolts.

d, Remove the front cover of the switchholu'd and raille the dl'sig-nation ~trip~ to permit the drop shutters to fall.

e. Swing the retrach.ble legs out ft·om the open end of th tl switch-bOllrd cover until the side bl'aces snllP inw the slots. Fit the hooks under tht'. Sf'at top into the holes in the angle brackets and fasten in place by means of the slide bolts fot' use liS an operator's chair,

/ . Install eight hatteries BA-30 in the compartment.9 in the lower hack of the switchboard (see fig. 3). If elttemal battery is to tM! used fm' the night alarm circuit , do not install IIny battery BA~'W) in the compartment designated NA BA 'fT,

g. Inspect the switchboard for damaged or loose parts. h. Connect the incoming lines to the binding posts mounted on the

protector panel at the rear of the switchboard (see fig. 4) , The first four line eircuits are equipped with simple.! coils for use when sim-ple.led telegraph circuits are desired. The telegraph legs are brought to four binding posts 00 the back of the protector panel alld are designated-

1 2 TELEGRAPH , ,

i. When two switchboards A and B are to be used together in ad-jacent positions and grouping ·is desired, connect the grouping cord CD-611 (fig, 4) of switchboard A to the receptn('\e designated GROUPING on switchboal'd B and connect the similar groUPinll cord of switchboard B to the receptacle designated GROUPING on swi«;hboard A.

j. When 110-volt , 50-cycle a-c is available, plug the Telering cnble into II. convenient outlet, Elltend ringing current from the Telering to the switchboard by means of the cord CD-4!i2. The receptacle for this cord on the switchboa,rd is located in the lower back and is designated POWER RINGING. The Telerill,l!: may be removed from the switchboard cover and hung up in a convenient location if desired.

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UNIVtl1'im OfUUfORN lA

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, SIGKA1, CORPS

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k. 'Vhen UO.volt, GO-cycle R-C is not llvailable, CO Il I' Cl'ter M- 2'22 IIllly be used. The opel'ation of this ringing converter' is covcl'ed i n TM 11-344.

l . Connect cOl'd CQ-258 to the GRD tCl'lninal on the lower part of the bllck of the switchboard lind to ground rod GP - 29 dth-cn into the ground.

7110. Plug a hC!ld and chllSt set HS-19 into t.he jack JK-.'17 mounted in the I I'ont. of the key shelf. T wo head nnd chest sets Il l"e nOl'mnlly .:an"jed in the COJllP:l nmcllt ~ pnwided in the front cover.

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., , 0.;. ".Iff"", UNIVE~\lTY Of CAlifORN IA

J

, 5. Switchboard operation.~The openttiou of ~w i'~hoo!lrd 13D_

91 is chanlclel'istic of cOInpar"hl() commct't; ial prllctice. It is to be Hnderstood that ill stAt ion-to-statioli coll tLections, trunk-to-statioll connections, etc. , u-!$odated front lind buck l;or(1.

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.--a. !neomblg calls.- Incoming calls on lines or trunks are indiclI. led

by (h'op signals. b. Amwering oolu,-Whcll It drop sib 'lull operates indicMing !Ill

i l lcoming ca ll , in!lel't an answeri ll);: (bnck) plug into the line or U'unk jack nssociated with the opera ted drop. 11 the cll ll is iu(.-oming over

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, SIGNAL CORPS a trunk circuit the jllck designated L should receive the answering plug. Operate the key associated with the cord being used to the TALK position (ll.way from the operator) and challenge.

c. Originating call3.-To make an outgoing call at the request of !I. station user, insert the culling (front) plug associared with the proper answering cord into II. trunk or line jack in accordance with the foll owing procedure:

(1) oaU to ~rl/tiq".-lnl!ert a calling (front) plug into the line jack of the desired fltation. Operate the key associnW with the com dr-cuit used to the Ilonlocking RING position (toward the Opel"Rtol'). 11 the swilchlxJ!l rd is supplied with puw('r ringing, open.tion of the key will ring the station bell. If no power ringing is available. it i~ necessary to operate the hltlld generator while holding the key in the RING position. In either case, afte,· each appliciltion of ring-ing cunent, opente the key w the locking TALK potiition and listen for un answer from the distant. end.

(2) can over comm.on battery 11/,(UI·jUll tntM.-Iu;;ert a calling ( front) plug into a trunk juck designated L. This will signal the operator at t.he dista", office. Operllte the IlSSOCillted key to the TALK position (away from Ihe opel"l\lOr) and IIwl\it the distllnt operawr's challenge.

(3) Coll over dial trunk.- Insert a ClllIing (front) plug into a trunk jack designated L. Operate the associated key to the TALK position a.nd listen for dial tOile. When dial tone is heard, plug the dial cord plug into the 0 jack associated with the selected jack, and dial the desil-ed number. Remove the dial cord plug and listen for ringing lone. It is not necessary to ring on the trunk.

a. Supervirion.-Supervision·is provided by means of drop signals located on the face of the switchboard directly above the associated cords. Ring-{)ff or recall is indicated by the drop shntters falling. ChalJen~ on t.he connection to determine whether the signal means disconnection or recllil.

e. ConferffIU callR.-To connect a numbt>r of lines together for conference pu~s, the conference circuit is utilized as follows: Insert the plug of an answering (rear) cord into the jack associated with the telephone of the person originating the conference. Then insert. the plug of the associated calling (front) cord into a confer-ence circuit jack. Make the other connections to the conference circuit with answering plugs inserted into the conference circuit jacks and the R!lSOCiated calling plugs connected to the desired line circuit jacks. Call each member of the conference in the usual manner.

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TELEPHONY. CENTRAL OFFICE: SET TO-I2 , f. Face equipment /reyH.- A strip of five turn-button keys is

mounted on the faoo of the switchboard at thp. lop of the right·hand panel (see fig. 1) . Th_ kPY!' an> cl~igllUtl'd NIGHT ALARM, RINGING, BATTERY, GROUPING, IImJ EXT BAT,I·espectively. Their functions are as follows :

(1) Night owrm kt y.-With this key turned to the ON position, an incoming call will cause a huzzer to operate when the drop signal falls. To stop th~ buzzer, turn the key to the OFF position. If the operation of the buzzer is not desiNld, leave the key in the OFF position.

(2) Ringing key.- With the key turned to the position designated HAND, ringing current must be applied through the use of the hand generator. With the key turned to the position desiglLnted KEY, the switchboard is prepared "for the application of power ringing current.

(3) BaJtery key.-Cord circuit and tnnsmitter battery are sup-plied from battery 1 or buttery 2. With thO! key thrown to position I, energy is supplied from battery 1; in position 2, energy is supplied from battery 2.

(4). GrOlJping key.- When two ttdjacent switchbollrds BD-91 are used together nil a single installation and it is desired thnt both boards be attended by one operator, operation of the GROUPING key 011 the unnttended switchboard to the ON position 1I1'l,";or i!!teli the cord circuits of Ihnt Ijwikhb"ard with the operator's circuit of the attended ltruction will be accom· plished in the following order : jacks, drops, keys, fuses, head and chest sets, batteries, and ringing equipment.

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Onq, ol",,", UNIVtl1'im OfUUfORN lA

SIGNAL CORPS

SroTlOS III

FUNt-'TIONING Qlo' PARTS Pa, .... l'h S_ltcbbollr

TELEPHONE- CENTRAL OFnCE SET TC--12

it cannot be used with telephones or circuits that require nn CJ[ternai source of tl"all~Ulitler current or that require direct current for super-viSOI1' purposes. The application of ringing current w this circuit from the line causef; the drop shutter w fall. When a plug is in-serted into the jack, the shutter is automatically restored })y mechani-cal means and the winding of the drop is disconnected from the line at the cul ·of!' contacts in the jllck. Contacts are ml'nished on the drop shutter wllich dOl;(' a night a larm circuit and provide, when desired, for un audible signal when a shutter hils. This circuit may be connected to the following types of equipment 01' circuits:

u. ~1ilitary loenl bRttery (magneto ) telephone such as telephones EFr-3. EE-4, EE----5, nnd EE-8.

b. CommercinllOCll.I oottery (mngneto) telephones. c. ,Magneto line circuits in switchboards BD-14, BD-71, BD-72,

BD-80, BD-89, B0-91, and BD-96 and in commercial switchboards. d. Line circuits equipped with r ing·down relays lind al'l'auged for

two· wily ringing in switchbourds llP-74 nud llD-78 and ill commer· fiR I switchboards.

B. Trunk circuit, dIal and common battery manual (fig. 6).-This circuit is for use with common battl'l'Y central office equipment of either mllnual or dial type. It may be conllected in place of any common baUery manunl or dial (automatic) telephone.

a. The application of ringing current at the distant end of the line call1les thc !ls.-;ucilltcd drop ~huttcl' to fall. A contact on the shutter

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SIGNAL CORPS

L'OnnecUl" ground to thl' NA lead to operate an lIudible signal. When an answering plug is iJlS(' rtM in the line jack, a circuit is c1~ to bridge the coil of the drop acrOss thl' line as a holding bridge. This action extends supervision to the central office and cuts off lutcmatic ringing current.

b. On outgoing common battery manual calls. the insert ion of too calling plug in the line jllck places the coil of the drop across the line which signals and extends Sllllel'visiull t(l the central office operator withuut the neeessity of ringing 011 the line.

c. On outgoing dial (autoffi ll.t ic) callR the insertion of 'the calling plug in the Jille' jack and the subsequent connection of the coil across the line seizes the centrll i office equipment. The operato]' then inserts the dial cord plug in the dinl jack which disconnects the coil from the trunk and closes a holding bridge for the trunk through the dial impulse springs (see fig. 6). The operator dials the desired number, causing the switch t rain at the central office to complete the con-Jlection. After the dialing is oompleted the dial cord is removed from the dial jack and the trunk is IIgain held through the drop.

tl. When the plug is removed from the jack upon oompletion of a call, the trunk-holding bridge is opened, signniing the central offiCI! operator in the case of a manual can and Rl10wing the centra l office equipment to releruse in the ca!!e of II dilll GIlII.

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9 . Cord circuit (fig. 7).-The;e cord circuits lire limited to use with magneto lines becllUse ringing current must be applied to at least one of the lines connected to the cord circuit in order to actuate recall or disconnect signaling equillment. This signaling equipment "oll",istl< of ",upt'rv i~ry drops. one of which is associated with each piliI' of cords. The drops lire local l'd in the face of the I)\Tit.

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TELEPHONE· CENTRAL OFF]{$ 81'1'1' '1'0-12 9--10

a. When, on incoming calls, the plug of the anHwering cord is inserted in the line jack, the supervisory sigllnl is bridged acrOSll the tip and ring of the line to provide for ring-off supervision. The operator answers the call with the TALK key in the operated posi-tion.

b. On outgoing calls the plug of the calling cord is inserted into the line jack. Upon operation of the ringing key, ringing current is applied to the line if the ringing machine is operating; if not, the circuit is prepared for the operation of the hand generator. Except when ringing, the TALK key is operated until connection has been made to the called line.

c. When a' conversation is completed, ringing current should be applied to the line by the telephone user or distant switchboard operator. The ringiug current from either source will operate the supervisory drop, thus providing a disconnect signal. When a com-mon battery trunk is associated with the cord circuit, ringing current for the operntiou of the supervisory signn] must be supplied over the magneto line which hilS been inl'olved in the trunk connection.

To CQrdC/d

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10. Ringing circuit (fig. 8).- This circuit provides a switching key and a receptacle to connect either hand or power ringing to th~ cord circuit. W ith the key in the HAND position, the circuit is prepared to supply ringing current from the hand gellerll.tor GN-4l. With the key ill the KEY position and the ringing machine (Tele-ring or ringing colwerter M- 222) connect-ed throngh the power ring-iag receptacle, the circuit is prepared to supply ringing current

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UNIVtl1'im OfUUfORNlA

10-11 SIGNAL C

TELEPHONE CENTUAL OFnCE ~El' TC-12 11_12

direct current tnlking battery to the operato!"s tnuIHmitter . . A var-istor is bridged IICross. the rect'iver tenninals w reduce the acoustic shock to the operator which might be caused by excessive voltaj!es. The va ristor consists of sn arrangement of ropper oxide disks the I'esistallce of which Ile("reases as the voltage increl!.ses, thus reducing the current through the roceiver. Binding posts for the eJl:ternl!.l battery terminals are mounted olJ,. the terminl!.l strip on the bottom of the protector panel. A receptRCle llnd IL terminlLl strip for the groupinj! ronnections are provided on the protector pl1.nel. The A2. 82. T2, and R2 lelLds extend the talking battery leads and the T unJ R leads of the com circuits t" the terminal str ip from the TALK key. The grouping rom (CD-6ll) is wired to the terminal strip lind is proviJed with a locking ping w connect to the grouping receptacle of an adjacent switchboard BD-91. The receptaele is conne.-:ted ro the ilOrnllllly open l"OntllCts of the grouping key SW- 179 by the AI , BI, Tl, llnd Rl lends. When the grouping key is operated the rord cll'cnib; of thllt swit chbolll"d are associnted with the opern-tol" S te lephone circuit , of an adja~ent switchboard through the AI, nl, TI, and Rl leads and the grouping cord 00-611. Head and chest set HS-19 mny be CQnnf\Cted to the operator 's telephone circuit by means of II plug PL--68 and the jack JK--37 located on the left

I front of the key shelf.

To Mog Line CIrt ..... '-,

To cora CM ":::::j To Trll C/l:t _ ..

11"''''' •• IO.- NIKhI . 1 •• ", ~I I"

I~II'I SIGNAL CORPS

minds are provided for an external battery. When an external bat-tery is used, no battery should be left in the compartment. The key which controls the operation of the night darm is located in the top of the ffU!e equipment.

13. Conference circuit (fig. ll).-This circuit consists of four jacks wired in p!lrdlel for conneding a maximllm of four lines to-gether for conference purposes. Cord cin:l1its should be used for connecting the various lines to the conference cirtlllit.

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14. Master schemaUc and wiring diagrams.-Fi.I!.'ure 12 ~hows all the varions circuits of switchboard BD-9J in schemati~ lm'm 11.11(1 shows their interconnection. F igures 18 and 14 show the wiring diagrams for switchboaTd BD-9l.

15. Main distributing frame.-a. The terminal equipment is mOllnted in the rear of thl.' ~witchboord. The arrnngement of the apparatus is shown ill figure 4. An opelliug with a cover is pro-vided ill the bottom center of the I'I!:nr door to permit the closillj,t of the door while the switchboard is in use. Four simplex coils C-288 are permanently wired in the first fOllr line circuits. The telegraph binding posts are mounted on the lower part of the pallel with the binding post.

h. Two vertical rows of 12 pairs of I-ampere fuses and 12 pairs of unit dischargers each are mounted 011 the protector panel. The unit dischargers oonsist uf two carbon protector blocks for each line wire, one block connected to the ground strap I\.IId the other tapped on the wire from the fuse to the drop. A definite air gap between the two blocks is provided by a thin spacer of insulating material. The air gap is large enough to insulate the normal currents in the line wire from ground but provides a path to ground for foreign voltages high enough to damage the telephone equipment. Two terminal strips., each of 24 binding post.

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16. Ringing equipment. - a. Po-tcer ringer, ff). cycie (Te/e-ring) .-The Teierillg 2O-cycle power rillb"Elr is II vibruti ng reed type of fl~uency converter. The reed vibrates oot Wef!1l 1\ cOntact screw Ilnd !til elect romagnet . The conillct screw is se~ at the fRctOry, and it is suggested t lmt no chllnge be made in tIle ad justment unless the reed vibl' lltes in !I sUI'ging 1ll,IIlllCr or' there is spurking li t the contact. If ~I)jr rking OCCUI'S, it requir-es on ly the sliglltest tunl 011 Il ,e contact IlCrew, ei lhf't· ill\v'lni 01' out-nlrd , to (:Ol'rect it. However, it. is seld om that allY c1IlHl,.~ will hi· n(!(.~'''''"l·y. The udjustn)(,llt of the Telering COllUtet i~ p ruclicltlly "pptlsi te to 111 11 1 o f uther I'ibntlillg type pow('r

OOgtr •• 1 If"", UNIVE~\lTY Of CAlifORN IA

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n'SH7 ""~ • • 18.-a ... l!~bbo • • ~ 1ID-9 1- .. lrhu: d lu •• mo 01 ..,,41. """ .... ' 0 ... tel~ph" .... ond

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ringers, iii tha t the contuc{ gap in the Telering must be kept a.! wide IU PQJJ8ible. Closing the contact gap does not inc,"ellse the output., but instead will up5Ct the adjustment, Cllusing sparki ng, illterfer _ ence with radio Nlecption, and may prpw'nt ~hll·tillg. (Sel' fig. 15.)

b. CQnverter M- 2£a.--CoII\'er tCI' M- 2:,12 is described in TAl 11-344.

IS

., OOgtr •• 1 If"", UNIVE~\lTY Of CAlifORN IA

I

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TELEPHON E CENTRAL on'to: SKT '1'0-12

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TELEPHOI'[' CENTRAL OFFI CE S I':T T C- 1 '1 "

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c, F it the fro nt cover in phloo lind fasten the switchboard by tight.ening the two t hurnbsc l"Cws (fig, ttl) ,

d , RemO\'e the b;ltte r ies fn)rn the bllucry (;omp8.l'tmcnt to pl'e,'cnt eOI'rosioll of the switchbonl-d,

fI, Separate the switchbonnl lind hase by ioosen itlg the wing nuts undernell th the switchbo):II'd, T urn the switchbo'II'd ups ide down to

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5CI..,114 -fli eii itnte packing the con!,; Ilnd eurd weights ill the cord OOIfi-J)nrtment.

f. Return the >;witchbon rd to it s nOI'nnd posi t ion and slide the buse o,'er it. T UI"II the s wilehiJooni nnd Imse ol'er und restOl""C the C}[teli-sion legs on the [mse, ClnllllJ the seat top in po!;ition to hold the !iwitchhonrd snugly inside the hllsc, The sw it chboard unit is then packed lind ready for Army trll nsport.ation (lig, 11),

., , 0.;.. ... Iff"", UNIVE~\lTY Of CAlifORN IA

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TEL!:PHONt: CENTRAL o~·nCE SET TC- 12

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c. Mainlt1l4nte equipment M E-Ml.

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L . ___ ... ------------- A~ _____ ___ ______ . __ 2 . _____ __ SA3(L ___ ___ Rauft}' •• • •••••••• + I . .... ___ ... _ ......... ~--- ---------- - -50 ft _____

-- --- ---- ---- Cord. ___ . _____ . _.

L ..... . . GRZ460IL ___ Copper, IOIderln. __ __ L . _____ _ 6Z400'2. ___ __ FlNbli&ht •• •••••••• '-. _ .. -.- &Qli ll S5-5 . .. H andle. ____ ________ L ___ ____ 6Z&896 ____ __ t...n>p with eK\.e ... i.,

~'" 32 _______

-- ------- ----Nut_. __ __ _____ ____

L ____ __ . 6R4513 _____ PI~ ______ __ ______

L ___ __ . _ 6R4e03 __ ___ ____ _ do _____________ L ___ ____

6R46~ _____ _ __ . _do ____ ___ ___ ___ L __ ____ - ---- -- -----.- 8ct.o ... ____________ 1 ____ ____

6RI62iO ____ Sere .. dri ver ________

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Bingl ... qe, 4-lb head. __ _ . ___ 8A-30. ______ ____________ ..

~78_ • . _. _._._+_ . __ ... + __

Rubber covered, ......, >-conduewr No. 18 A WO.

Without bandit!, M-Ib. __ _ • __ ._ TL--I22A _________ ___ _______

Wood, ~" . for IIOldering mm ___ IIG-w,.U, l 20-vol t "ith :M-ft

cord equipped with pl UI!I of 8I'pan.ble t ype, EdMon !>Me.

Un, fOf" ' 8--32, electr-o--pJv&-ni-'..

TI.....-13 ____ _______________ ._ TL-103 ___________ ___ __ ____ TL-126 ________ _____ ___ __ __ £lee .. , ~" _ tr,c ... .,*, __ ___________ TL-16~ _______ _____________

"' .... Iao! ....... I M .... r .... ..,...·. • ....... c_ dn_1no No. """ :00_. -,'.---.. ---- -- -------- ---- -------- -- .. _-_ ....... SC-A-~ C. ... . . ....... --- -.- ------ 8C- A- &48- F.8 c-

D-6U )..-C.

o. £. CO. ___ T)·pes-J •..

.-.--_ .. ---- ------------------------ . __ ......... -------- ---- ---- --------O. E. CO ____ iXU2 _____

. --- -- ----- -- ------------------ -- --- - ---- ---- --- - ~C_A-6M__D. -------_._-- ____ ••• _. ___ SC-A--M3-B. ------ ---- --

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d. Head and eh~8t Itt HS- J9.

llloell No, N_ -~ ' .... l;>tlon -4B41S _____ •• __ CbeHt uniL .. ... T- 26, ~- of ", foHowins ltema

(atoek number In p&rentheees): (4U924.) ____ _ ._ Strap. _ .. __ .. .. ST- :U. (~Z6925) ___ __ ._ • __ ._do ..•••• _ •. ST-25. (3Z8I1S). ..... Switch ......... !:IW- IIS. 3E333 . •.• .•. •• Cord .......• "". CC-333. 6-'oot, a-conductor. 3E331 ___ ...... •••• _do._ •• _ ••. _ CG-337. 2O-lneh. 2-oonduetor. ~C4153BA . _ . - Head band . . ___ • ~C4U3BA/l _ .. Pa.d_. __ _ • __ •• • _ Leather. ~B23M ...... __ Plug ___ •• .. _ • •• PL -58. ~B25Z2 .. __ ... . Recelver •••• __ •• R-22.

20. List of manufacturers and their addre88es. ---

Abb ... viation Name Arldru;o

A. E. Co_ •• _ Automatic Ele