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Research Department

Work c~~ried out by:

D~ Byfield. D., Maurice" ,

.; .

~)RT NO~ 0(1035

iieria1 ' No:'" 1945/21.

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June l~45. R.LoT.;R.4

. H~lt, Vo Iv10DEL 650 RECE;rVERS. .,' -'-iJhos"sis ' NoS.; "'013599 and' 0019'87': " , ' .' - " "

This el even v8.1vEl domestic broadcast roceiver is one of "tho' bo'stBr1t1'sh receivers in the moderately expe~s1ve class which could be purchased befor~ the war. It is intended to give the purchaser the possibili ty of' , '~ b.1gh . fideli ty listening coupled with f!3:1rly good short:--wo.veperfpI'Illa~ce for dist·e.rit . stationrccept;i.on. tha v~8'Ve' length's covered are ;tong wf3ye{3, mediwn wnves aria .the 'short wave bands from 4. 9 metres ' to 107·met".r:es~ · It has one, eiftptic ioudspeaker, ' B 2 positi9lf.irite:cin~diate f;equency~~iect'ivi.tY ' ' ID-i1tch an'd twO" .' tone bo'nttqls' g;tvirlgP9ssible bass cut and ~;re,ble " ,cut~1wO chassis were moasured bocause: bhassls"N6. 013599 is not typlcai 'b't tli'ese " " raC13i vers as:' 'i t '~I~s' ai te~'ed by the G~amo'phone OOmpany Liini ted ~w1ng to ' a BBC request for bettero-·than- usual 81gnal/Noise rat10s. .. .. , : .. .. ,. ', :':. '.. . _,

The tests' made 'Oil this rec'eiver' co'nfoI'm to Resea rch Re~rt, G. o~4., ulll.,ess otherwise stated.

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If ' tiie r'&sponse 't 'o a mbdula tion f~equencycil400 cycles . he t~~~n . as '~z'ero :'. decibels, . t ,h"en tiie ' .frequencies, at whIch,' thi~~ Fesppns'e'f1~~~~rt-e,n~'tp ,~D~ db . .. are 48 cycl'os per s'Elcond nnd' 1 , 400 'cycles per second"with {3. dummyload 1n placp of the l ourlspeflker spoech c01l and the tone controls at minimw:,n ~op.' , ,m.aximwn bass and the high fidelity .switch in the high selec t ivity posit'1on. . ' :tn ' the same conditions as above but' wi ththe . t 'onecoritrols in .the, -mi-nimwn t op m1nimwn bass positions ,the 'lroquenc ie~ ,f;'~ -6 , dbo a?~ 16Q' ,~ycles. p~r: ~ecop.d and 1 , 900 cycles per 's.econa: :: Jp. tb,e s~me : .9o.+idit'ions". as bo'fore but with '., the ;tono controls in the mnx1fuUm top '~xirnwn bas~pPsi'ti.o·ns , the' frequeI1cies fl t w~i:ch ' the rospons'e hos . frillGn . to -6 , db. ~re '6'5 ' cyoles: "per sec~!l.d. 6,!l?- . 2,QOO cY91es per second. vi ththe .'iligh fi dell'ty' switch in" the' hfgh t1,deli ty ,pt?sition 8:~c1 thetone ,cont.rois i n t~e maximum top and minimwTl bass posi t i'ons , th~ . f~oquencies a t which the response ha s full on by -6 db . are 65 pycles per saconc1 l.Uld 4 ,000 ' cycles per second~ W1 th the dummyload

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removed and the loudspeaker speech coil replaced and the high fidelity switch in the high fidelity position an:dthe tone controls in the , maximum top and minimum bass positions, the frequencies at which the response has fallen by -6 db. are 60 cycles per second and 6,000 cycles per second. ', ", It will be noted that ,in "the high fidelity pos1 tion, this receiver response falls far below tha~ of 'J;b.e :Murphy .A. 40. C Rece1 ver described in Research Report G~03:3. Nonetheless, this receiver sounds quite pleasant when listening in the l;ligll, tideli ty posl tion to sui table pI',Q'gp~es. , The absense of the somewhat a:l~z1'1hg treble response of the MurPhY"~~'40. C 1s probably due to the fact that the H.M. V, 650 response falls ,01'·1' rather more ' gra-du,ally at the higher frequep.c,ies.

2.2 Sensi;ivity.

Th1s 1s good and is better on chassis No. 013599 than on tb.e more standard models,- the improvement over the "standard model being of ~he order of 3 ' - 6 d.b. Excluding the , short-wave band cover1ng 21 - 55 megacycles, the average ~nput m1crovoltage modulated to 30% by 400 cycles .requlr.ed to produce a 20 db. S1gnal/Noise ratio a t the output is 30. The sensitivity in the 21 - 55 megacycle band 1s very 'poo~ and is of the order of ,300 m1crovolts.

2.3 'electivity.

The long-wave selectivity is somewhat better than that o~ , the medium wave band due to high 'intermediate frequency. The medium wave s~l~ctivity figures are a. ' follows:

With the high fidelity switch in the selective position and tone controls at :maximum treble and maximum bass responses the band wid~h for ... 20 db. 1s ' ' .:!: ~ kC/s. With the high fidelity switch in the highfidel,ityposit:ton and the4tonoc,cmtrol.s" at Il1 .. ruimum treble and maximum bass responses, the band width for -20 db o is + s§. kC/s. For -40 db. the band width is + l~2 kc/s.

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The A.V.C. is poqr. There' is no threshold as the A.V.C. ' de+ay volts are insufficient to prevent the amplified random fluctuation noise from, the first circuit and valve .from oper:at1ng the i...V.C~ diode. J'urthermore, the receiver has 'not been designed with a view ' to so arranging the audio gain as to prevent ~verloading the audio valves when strong signals ar~ being received. '

2.5 Jmdio Input~OUt;put Charac_~.stic.

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The mnxiIilurr;. undistQrt.QJ. ~I!owor output. is 4 watt.s, 'the maximum put put is 9 watts~ " 'lb.G ·opornt.i011 of! . t his cune botw.oon 'zero' watt's ' o)J,t and the maximum undistortod value is very linear i,Ilclic fl tinG that harmonic 'distortion should be low in this range.

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T§TS ON RECEIVlrR /. " . . .. " ., . ... . . .

RL 36 H.M. Vo, 600 ' Chassis No. 013599 and OO~967 • .' • I ~. .' ~.: '. :

tChas s'is No~ .013599 was modif1ed by i.M.,I. : to 9b,ta1n maximum . ' Signal/No1se rat'10 possible with reas~nable' seiecUv1ty)

Long Wave 7l0m. - 200Om. (4220 5 kC/so - 150 kC/s) ,

redium Wave 193.7m. - 570m~ (1550 kC/so - 526 kC/s)

tJ.VI.l 33. Sm. - 107m. (S" 9 'M;c/s - 2.8 MC/s)

S.W.2 1l.28m. - 34.2m.t26~5 ' MC/S ~ 8.7 MC/s)

S.W.3 4 .. 875 ... l5.47m. (61.6 Mals - 19.4 MC/s)

,CONTROU

Yac1ng panel : lef'C to right

1) Top control ~) Volume control v) Tuner 4) Wavechango switch 5) Bass control and ON-OFU switch

POWER SUPPLY. 195V .. , 255V A.C 0 i

APPLIED VOLTAGE. 22OV. Ace.

INTERMEDIATE FREQ,UENCY. 465 kO/so

~EECH COIL RESIST.£NCE. 4 ohms.

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Thi. drawlnA't8lth1t.p'OtDel'ty m.jJa. HLT ...... (3

8"OADCASTING CORttORATION, ."cl may not be reproduced or disclosed to • thIrd party In any form without the writteft perm'Mion of the Corporation.

I/.M. V. 650 RL.T.R. 4 .

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WIGHTMAN MOU NTA IN. LTO .. •• TIL1_ERY House:. A RTILLERY Row. W eSTMINSTeR. S . W .1.

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