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ViceroyMkIV

KWElectronicsLtd.

Ca.1964

NotesbyGwynGriffiths,G3ZIL

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RestoringaKWViceroyMkIVHFsinglesidebandtransmitterGwynGriffiths

ThisKWViceroysinglesidebandamateurbandtransmitterwasboughtviae-bayinNovember2009.ItistakentobeaMkIVbecauseanantennachange-overrelayisfitted.Whilethefrontpanelwasindecentconditionfromthephotographsanddetailson-line,theinternalswereratherpoor.ItwascollectedfromWitney,OxfordshireonourwaybacktoSouthamptonfromNorthWales.Thesellerwasahouserenovator,andinalargeshedatthebackofthehousetheywereworkingonweretheremainsofanextensivecollectionofelderlyamateurradioequipment.Atonetimetheequipmenthadbeenlookedafter,butfromappearance,forsometimetheshedhadbeenunheated,damp,andwithmiceaswell.ClockingmyinterestinaTaylorModel68RFsignalgeneratoroflate1950svintage,theselleracceptedanofferof£10,andthrewinapowersupplyforaKWVespaMkIIwithitscardboardcoverfornothing.

PowerSupply

Thepowersupplywasinfaircondition,withnoextensivecorrosion,Figure1.Giventhesimplicityofthewiring,andwhatIfeltwasthedefiniteneedtoreplacethehighvoltagecapacitors,itwascompletelystrippeddown.Thiswas,ofcourse,afteracircuitdiagramhadbeendrawn,asanexactcorrespondencewithpublishedcircuitswasnotpossible.Forexample,singlediodes,notmultiple,wereusedineacharmofthe750Vsupply.Carefulnotesweremadeofthetransformerwiringcolours.

Dismantlingstartedwiththe“750V”tagstrip,followedbytheassociatedcapacitorsfromtheirclips,themainsvoltageselectorpanel,the“750V”

Figure1.Powersupplyunitremovedfromthecase,inasreceivedstate,havingbrushedofftheworstoftherustonthetransformersandthesmoothingchore,rearcentre.

Figure2.Powersupplychassisstrippeddowncompletely,beforebead-blasting.

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transformer,mainscableanditstagstrip,andthenthethreefuseholders.Therustedsmoothingchokeforthe“350V”supplywasremoved,measuring3Hinductanceand75Ωresistance,markedwitha200mAmaximumcurrent.Thedetailswouldbeinscribedonthecleanedandrepaintedshroud.The“750V”transformerwasdismantled,notingthatgreenconnectedtothe200Vtagonthevoltageselectorpanel;yellowto220Vandredto240V.Thelooserustwascleanedoffwithafileandcarbidepaper.TherefollowedtreatmentwithKurustrustconverterfromHammerite,beforespraypaintingwithagreyaluminiumprimer,whichmimickedtheoriginalfinish.Asilverpaintwasusedonthemetalclampofthechoke.

Thewireloomtothetransmitterchassispassedthoughaperishedrubbergrommet.AsmearofVaselinehelpedextractthewires.Alltheoriginalgrommetswerereplaced.Theremainderofthewiringandtagboardswereremoved,andfinallythe“350V”transformer.Thiswasgiventhesametreatmentasthe750Vtransformer.

Withallcomponentsremoved,Figure2,thechassiswasbead-blastedclean.Anearoriginalfinishwasachieved.Allofthemountinghardware,thenuts,bolts,set-screws,voltageselectorpaneletc.werecleanedinanultrasonicbath.Thosethatwererustywerefirstsoakedinacitricacid-basedcleaner(HammeriteRustRemoverDip),andadilutesolutionwasusedintheultrasonicbathforafinalclean.

Thethreehighvoltageelectrolytics(two50+50µFinseries/parallelforthe“750V”supplyanda32+32µFforthe“350V”supply)werereplacedwithnewF&TWestGermanunitsratedat500V.New330Kbalancingresistorsacrossthe“750V”supplycapacitorswerealso

replacedastheyhadincreasedinvalueandwerenolongerequal.Theelectrolyticinthebiassupplywasreplacedwitha47µFwireendedtype.

Reassemblywasstraightforwardusingthephotographsandmydrawncircuitasreference,Figure3.Aftercarefuldouble-checkingthesupplywasswitchedon,andthevoltagesmeasured.Allwasfine.

Asof2018thepowersupplyhasproventobeentirelyreliableontheoccasionsthatthetransmitterhasbeeninuse.

Figure3.Therestoredpowersupply.ThethreecapacitorcansinbluearenewF&TWestGermanunits;alsonewisthemainscable.

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TheTransmitter–Pre-restorationchecks

Withthepowersupplyrebuilt,thetransmitterwastestedas-is,asitismycustomtotestbeforedisassemblytoensureasfaraspossiblethat,whenrebuilt,anyfaultsorproblemsfoundwereduetoincorrectreassembly.

Thetestproceduregenerallyfollowedtheinstructionmanual1,andcomprised:

1. Allvalvesandallcrystalsinplace.

2. Visualcheckonallofthevalveheatersglowing–foundallOK,includingtheneonstabiliserontheVFOchassis.

3. OntheStandbysetting:checkonthe“350V”HTvoltageincaseitwasbeingdraggedlowthroughexcessivecurrentconsumption–foundallOK.

4. 50Ωdummyloadconnectedtoaerialsocketatrear,viaaHansenSWRmeter.

5. StillinStandbymode,gridcurrentwasobtainableonallbands.PeakablewithMixerandDrivercontrols;peaksonMixerinputaboutwheretheyshouldbeonthefrontpanelscale.

6. MovetoTuneposition,biaspotentiometeronpowersupplyadjustedtogivePAanodecurrentofjustlessthan50mA.MovetoMOX,andwithswitchinSendposition,adjustedto50mA.AllwellwithPAwhenHTappliedwithnodrive.

7. Becameobviousatthispointthattheglassinthemeterwasnotproperlyattached.I’vefoundthisacommonproblemwithelderlymeters,wheretheoriginalgluearoundtheglassedgeshasbecomebrittle.Notemadetorepairwhenstrippeddown.

8. Beforeapplyingdrive,lookingatthePAtunevariablecapacitor,atsomepositionsthevaneswereveryclosetogether.Notemadetoinspectwhenstrippeddown.

9. InTune,withdriveapplied,outputobtainedonallbands.

10. Audioinputtothemicrophonesocketproducesoutputasexpected.Looksverygoodatthisstage,stripdowncanbegin.

TheTransmitterChassis

Theuppersurfaceofthetransmitterwasinratherpoorshape(Figure4left).Therewereextensiverustypatches,andevidenceofpittinginthoseareas.Therewasclearevidencethatmicehadbeenactiveontheupperchassis!ThisViceroytransmitterunitcomprisesthreechassissections,inadditiontothepowersupply:thesinglesidebandgeneratorunit;theVFO,oscillatorsandmixertogeneratemultibandsignalsandthePA,VOXandaerialchange-over.Ofthethreesectionsontheuppersideofthechassis,thePAwasleastaffected,theVFO,oscillatorsandmixerbeingtheworst.Incontrast,theundersidewasinrathergoodconditionthroughout(Figure4b).FromtheconditionoftheundersideIfelttherewasnoneedtodismantlecompletely,aswasdoneforthe(simpler!)powersupply,

1 AnelectroniccopyisavailableontheKW_RadiosYahooGroupathttp://groups.yahoo.com/group/KW_Radios/files/

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butwouldproceedtoseparatethethreechassissections,disconnecttheirinterconnections,andclean,treatandpainttheuppersurfaces.

Todismantlethechassis,thescrewsbetweenthefrontandsidepanelbracketswereremoved,andbetweenthesidepanelsandthechassis.Thesix4BAsetscrewsandspacerwashersholdingtheLshapedbracketattherear,acrossthethreechassisunits,wereremoved.Allthismetalwork,screws,nutsetc.weretreatedwithHammeriteRustRemover(citricacidbased).

Allknobswereremoved.Themicrophonesocket,astandard4-pintypetoincludeaudiosignalandPTTswitch,wasnotoriginal.Thiswasclearfrom(a)theratheramateurwiringofthePTTcontactsbetweenthesocketandtheSendswitchand(b)thescuffmarkswherethelargenutattherearofthesockethadbeentightenedwithalargespanner.Thissocketwasremoved,withtheintentionofreplacingwitha¼”jack,aswasintheoriginal.Todothis,thenutoftheaudiogainpotentiometerhadtobetemporarilyremoved.Analuminiumadaptorplatewasmadesothata¼”jacksocketcouldbefitted.

Thechassissectionscouldnowberemovedseparately.

TheSidebandGeneratorChassis

First,asketchofthelayoutoftheuppersurfaceofthechassiswasmade,showingthevalvelocations,thelocationsofthecrystals,andthewirecolourstoeachoftheconnectionposts,ontheuppersurface,andthesixonthesideofthechassismatingwiththeVFOandmixerchassis.Anotewasmadeofthecablesthrougheachofthetwogrommets.Particularcarewastakentonotethepositionof

Figure4.Left:Asreceived,upperchassis,showingextensivecorrosionoftheplatedsteelespeciallyonthecentresection.Right:incontrast,theundersidewasingoodcondition,anddidnotneedarebuild.

Figure5.Thesidebandgeneratorchassis,disconnectedandreadyforcleaning.

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thetwo435kHzcrystals,asoneisaseriesresonanttype,andtheotherspecifiedforoperationwith30pFparallelcapacity.AsketchwasmadeofthewiresthathadtobeunsolderedfromtheNet/CarrierInsertionpotentiometer,andthescreenedcabletoatagstripontheunderside.

Thecleaningmethodemployedwasfirst,useasmallbrasswirebrushwiththeinletofthegaragevacuumcleanerheldcloseandadustmaskworn,second,emerypaper,againwithvacuumanddustmask,andthenagelHammeriteRustRemover,appliedwithasmallstiffbrushorcottonbuds.Thiswasleftincontactforanhourorso,andthencleanedoffwithcleanwater.Theworsepatchesneededasecondtreatment.AHumbrolsilverenamelpaintwasthenusedinseveralcoatswithfineemerybetweencoatstohelpsmoothoutthepitting.

TheVFOandMixerChassis

Aswiththesidebandgeneratorchassis,asketchwasmadeofthelayoutattheoutset.Theflexiblecouplertothemaintuningcapacitorwasremoved.Whileanoteofthedialsetting(3.9MHz)wasmade,thesettingoftheVFOtuningwasinevitablymovedduringcleaning.Acoaxcablewithitsinneronlyconnectedtoafeed-throughonthesideofthePAcompartmentwasdisconnected.Thethreeself-tapscrewsconnectingtothePAchassiswereremoved,oneproveddifficultandwaslefttosoakwithWD40.ThewirestothePAchassiswereunsoldered;thearrangementinthe‘powerdistribution’screenedcompartmentwiththepowersupplyconnectorwasnotedwithcareasseveralwiresofthesamecolourpassedthrough.TheJonespowersupplyplugwasthendetachedaswiresfromitwentthroughagrommettothePA.

Thefivecrystalsclosetothefrontpanelwereremoved,notingtheirpositions:4965kHzHC6U

Figure6.TheVFO(uprightboxatright)andmixerchassis.Thiswastheworstaffectedunit,especiallytopleft.

Figure7.ThePAchassisontheleftbeforedismantling,showingthewiringloomaftertheVFO&mixerchassisandsidebandgeneratorchassishadbeenremoved.Thestateofthebackofthefrontpanelisalsovisible.

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closetothepanel,thenarowofFT243types,fromthepanel:6000,6250,8025and8175kHz.Allwerecleanedinanultrasonicbath.Thechassiswascleaned,thenpaintedusingtheproceduredescribedabove.

ThePAChassis

ThePAchassiswasinfairshape,Figure7;alsovisibleistherust-stainedrearofthefrontpanelwherethechassisandsideplateshadbeenincontact.TheEddystone898reductiondrivemechanismanddialwereingoodcondition.Whendismantlingthisstage,carewastakenaroundthedrivecordtothepointerofthedial.TheJonesplugcanbeseenwithsomeofthewiringstillattached.

ThePAcompartmentgauzewasremoved,thenthesetscrewsfromthefrontpanel,exceptfortheonebythePATuneknob,followedbythescrewstothesidepanel.ThefixingnutforthePATunecapacitorremoved,allowingthetuningcapacitortodropaway.Theleadstothepanellightswerecutclosetothebulb-holder,andtheEddystonedialremoved,withitsfixingscrewsandspacerpillars.

ThePAtuningcapacitorcouldnowbeexamined.Acirclipthatshouldhavebeeninaslotontheshaftwasmissing.Thismeantthattherewasexcessiveplayinthefore-aftdirection,causingthenear-shortobservedearlier.Havinganexactsparecapacitoravailable,theentireunitwasreplaced.(InJanuary2018thecapacitorhadtobetakenapartandre-tightened).TheN750KceramiccapacitortothefeedthroughontherearofthePAcompartmentwasremoved,followedbyabarewirefromtheneutralisingtrimmertoafeedthroughonthesideofthecompartment.Thefiveself-tapscrewsholdingthePAcompartmentscreentothechassiswerethenremoved.Afterunsolderingthewiretoafeedthrough,thesmallALCchassiswasremoved.Next,thecoverovertherelaywasremoved,cleanedandrepainted.ThePL259aerialsocketwasremoved,notingthesoldertagposition,thecorrodedscrewsweretreated,andthesocketitselfcleaned,followedbythesameprocedurefortheoctalauxiliaryconnector.

Ruststainsontherearofthefrontpanelwereremovedfirstwithemerypaperonasmallelectricsander,followedbyrustconverter,andspraypaintedwithagreyprimer,Figure8.Allthiswasdonewiththefrontfacerestingonaflatsurfaceonasacrificialprotectivecloth.Thefrontpanelwascleanedwithakitchencleaningproduct.

Figure8.Left:thefrontpaneland,right,therearofthefrontpanelbeforecleaning.

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ReassemblyandTest

Thenotesmadeduringdisassemblywereusedinreverseordertoguidethereassembly.Theoriginalwiringloomwascleaned,endsofthewiresweresnippedandrestripped;inalmostallcases,therewasmorethansufficientlengthtodothiswhilekeepingtheoriginallayout.Inafewplacesnewwireswereused.

Thejobhadbegunon30December2009,andnow,on21March2010therestoredViceroywasreadytotest,Figure10.Withpoweron,andsettoStandby,alldiallightsandvalveheaterswereglowing.TherearcouplertotheVFOtuningcapacitorwasslackened,andwiththedialat3.600MHz,thecapacitorwasturned

independentofthedialshaftsothat,withaslightcarrierinsertion,thecorrectfrequencywasreadbyafrequencycounter.However,themixerinputknobwasnotatthecorrectpointcomparedwiththeprintedscalewhenatapeakat3600kHz.Theknobwasslackenedandadjustedsothatthepeakreadcorrectly.Adequateindicatedgridcurrentcouldbeachievedon3.5,7,and21MHz,butwaslowon14and28MHz.

However,onboththesebands,therewasenoughdrivetotakethePAanodecurrentto200mAmomentarily.OnTune,allwaswell,loadingintoadummyload.

Thefollowingweekendthetransmitterwasalignedasperthehandbook.Overall,littleadjustmentwasneeded,exceptforthecarrierbalance,seebelow.FollowingSection6oftheManual,thesearemyshortnotes,wheretherearenonotes,allwasaspertheManual:

Figure9.Reassembly:thepaintedpanel,theEddystonedialrefitted,andthePAchassiscleanedandreplaced.

Figure10.TheKWViceroytransmitterfullyassembledafterrestoration.Allvalveandcrystalscreeningcanshavebeencleanedusinganultrasonicbath.

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6-2(2) DoubledcheckedthatthetransmittersideofR69wastemporarilyshortedtochassis.

6-2(3) ThecoaxtotheVFOboxisaneasypointtotemporarilyshortthissignaltochassis.

6-3(3) Measuredat2.4Vpeaktopeak,so~0.8Vrmsasrequired.

6-4(5) 1.4VwasobtainedatthejunctionofR9andR10oftheaudioamplifier;morethanthe1Vprintedinthemanual,andcertainlymorethanthe0.6Vpencilledin.

6-5(1) Easiertogettowaspin7ofthe435kHzamplifier,whilethecoresofIFT1-3wereadjusted.ThebottomcoreofIFT3wastheonlyoneneedingsignificantadjustment.

7-4(4) 3.7Vpeaktopeak(~1.2Vrms)wasobtained,themanualshowed1.5V.

9-4(8) Theadjustmentpotentiometerwasrightatoneendandaproperdipcouldnotbeestablished.ThematcheddiodesthatplugintoaB7GsocketwerereplacedwithapairfrommyoriginalViceroy.

Theoutputsignalwithamicrophoneconnectedwasfinewhencheckedonareceiver.AnoctalplugwaswireduptoroutetheAnti-TripandmutingwirestomyStarSR550receiver.

Thefinaltestwason-air.Andsoitwasrealdelightthaton2April2010Imadetwocontactson14MHz,withRW3XZinMoscow,andSO8ZHinLublin,Poland.Bothstationsreportedagoodsignalquality.ThesecontactsweremadeusingmyMosleyTA31jr3-bandtrappeddipoleintheattic,anaerialthatdatedbackto1967.

Refinishingthecase

Thewrap-aroundcasewasnottoobadlyrusted;mildcorrosionwaslimitedtoafewareas.Thefinishwasasmoothgrey,notahammertonefinish.Givenpreviousgoodexperiencefrompowder-coatingspecialistsA1PowderCoatingatWoolston,Southampton,thecasewastakentothemforpainting,inacolourveryclosetotheoriginal,Figure11.

Figure11.TherestoredViceroyMkIVwiththeoriginalfrontpanelanditspowder-coatedcase.

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Postscript

AKWViceroyMkIIIawasthefirstpropertransmitterthatIusedasGW3ZILin1970.Previously,Ihadbuiltaone-valve7MHzcrystalcontrolledCWtransmitterwitha6L6asCOandPA.Thiswasratherneat,with,ononechassis,apowersupplyandthetransmitter.Therewasanex-WDmeterforanodecurrent,andoutputtuningwasviaapicouplercircuit.Therewasnocase,onlyachassisandfrontpanel.

Throughthegreatgenerosityofmylatefatherandmother,IjoinedtheSSBgeneration,where,withtheViceroy(£100secondhandfromthemakerKWElectronics),aStarSR550doubleconversionamateurbandreceiver(alsosecondhandat£40),andaTA31jrthree-bandtrappeddipoleataheightof~30’,Iwasableto“worktheworld”fromanexcellentsiteafewhundredmetresfromtheseaatHolyhead,NorthWales.Myfirstlogbookhasgonemissingovertheyears,butthesecond,fromOctober1970onwardsisstillwithme.

MyViceroystayedwithmeforseveralyears,butbecameneglectedinthelate1980s/early1990swhenitlivedinadampgarage.Itwasscrappedanddismantledsometimeafter1995,butmostofthemoreusefulcomponentskept.Inreality,itwasprobablyinnoworseshapethanthisexample.Ishouldhavekeptit,butc’estlavie,thisonehasbeenbroughtbacktoarespectable,workingcondition.

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UpdateJanuary2018

SincetheoriginalrestorationdescribedaboveI'veboughtasuiteofmoderntestequipmentthathasallowedmetorevisittheViceroy'salignmentandperformance.Butithasalsoledmedownanumberofblindalleys,atleasttwoofmyownmaking.Thesearealsosetoutbelowasareminder!

Lowpoweroutput-ASaga

Thiswasalongsagawithtwoblindalleys.MeasurementswithmyRigoldigitaloscilloscopeshowedthat,evenon80metres,Iwasonlygettingabout6Woutforover100WDCin.ThisconundrumwaspostedontheKWYahooGroupasfollows:

I'vereachedthepointwithheadscratchingandnosolution...Tome,theproblemappears(andIstressappears)tobedowntosomethingreducingtheeffectivePAanoderesistancetosomethinglike700ohmsratherthanthe2200orsoohmsthatitshouldbe.Herearesomeotherobservationsinnoparticularorder:1.ThecapacitortotheALCcircuithasbeendisconnected-nochange.2.I'veswappedthePAanodesRFchokeforanotherViceroyoneIhappenedtohave-no

change.3.Theproblemistherewiththe6146sthatI'vehadinthetransmitterforyears,andwith

thenewChinese6146sthatI'vejustfitted.4.On"Tune"on80mtoadummyloadIcannotloadtothe170mA/140mA(off/on

resonance)asinthehandbook,bestis170/120.5.Gridcurrentpuzzledmeforawhile,asIstarttogetgridcurrentwiththegridsbiassed

at-67Vwhenthedriveatthegridisonlyabout48Vpeaktopeak,soveryfarfromdrivingthegridspositive.Rather,atthislevelofgriddrivethereisanincreaseinthethirdharmoniccontentofthedrivewaveformfromabout-53dBrefundamentalwiththemeterbarelyshowinggridcurrentto-41dBat0.5mAgridcurrent.Ihaveconvincedmyselfthatthis"gridcurrent"isduetotheassymmetricwaveformratherthan"real"gridcurrent.

6.I'vetriedthe"cold"methodofcheckingthepitankcircuit,withahomebrewdirectionalcouplerconnectedacrosstheloadingcapacitorfedbyatrackinggenerator,a50ohmload,andlookingattheoutputonthespectrumanalyzer,andhavingfittedat2200ohmresistorfromanodestoground.Icaneasilygetvirtuallyzeroreflectedpower.But,fromthetablebelow,Idon'tthinkthecalculatedloadcapacitorvalueslineupwiththepositionofthecapacitor.Thismaybeaclue...

Thekeymeasurementsofthevoltagesatthegridofthe6CL6driver(inblue,ACcoupled)andthegridofthe6146BPA(inyellow,DCcoupled)areinFigure12on80metres.PAgridcurrentwasbeingshownonthemeter,butthePAgriddrivewasfarfromzero.However,thegainlookedreasonableat~57.

Tocutaverylongstoryshort-BlindAlleyNo.1-I'ddamagedbothoftheRigolscopeprobesontheirx10settings-inuseheretominimisecapacitiveloading.InallprobabilityIhadusedontoohighacombinedDCplusACvoltageandblownthecapacitor(ca.7pF)acrossthe9Mresistorwithintheprobe.ThismeanttheprobewasreadingthecorrectDCvoltage-asin

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thenegativegridbiashere,butwasonlyreadingsome30%oftheACRFvoltage.So,inreality,thegridsignalherewasreachingzero.And,aspowerisproportionaltoV2,30%ofvoltageissome10%orpower,so,unknowingly,Iwasgettingabout60Wout.

AllthiscametolightafterI'dpurchasedhighvoltageax100probe("2kV",5pFand100M).However,eventhatprobehasquiteaseverede-ratingofDC+ACasafunctionoffrequency,Figure13.

Withthisnewx100probe,afteraligningthe2ndmixeranodeanddriveranodecoils,tobesurethatthedual-gang15pF"Driver"tuningwastracking,Icouldget200Vpeaktopeakatthe50ohmdummyloadonMOXon80metres.However,theoutputforeachofthehigherbandsdroppedawaytonothingon10.Thencame

mysecondBlindAlley.

TheoutputwasdroppingawaybecausethedrivetothePAgridwasmuchreducedonthehigherfrequencies.Withasignalgeneratorinputtothegridofthedriver,measuringitsamplitudetherewithax10probe,andmeasuringthevoltageontheanodeofthedriver(afterretuningtoaccountforthepresenceofthex100probe)thegainat3.7MHzwas~66butonly26at7.1MHz.Nowgainshouldbe

givenbytheequation:

Figure1280metresPAgridvoltageDCcoupledinyellowanddrivergridvoltageACcoupledinblue.WhywastheregridcurrentbeingdrawnwhenthePAgridvoltagewasnowherenearzero?

Figure13Voltagederatingcurvewithfrequencyfortheunbrandedx100scopeprobe.Notethecuriousfrequencyscale;besttoratetheprobeat100Vrmsabove3MHz.

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gain=gm*Qloaded*2πfL

wheregmisthemutualconductanceofthevalveinA/V,inthiscase0.008(8mA/V,asmeasuredonmyvalvetester;anew6CL6shouldbeabout11mA/V).Qloadedcanbeestimatedfromtheratioofthepeakfrequencytothe-3dBfull-widthbandwidthmeasuredusingtheRigolDSA815.L,thecoilinductance,wasestimatedbynotingtheresonantfrequencywiththedrivervariablecapacitorfullyopenandfullymeshed,takingthedifferenceas15pF,withthevaluesoftheotherknowncapacitorsandacalculatedstraycapacitance,andusingamanual-inspectionoptimisationoverthe80-40-20metres.

Theinductancevaluesfor80-40-20were:29,9.4,2.3µH.Qloadedfor80-40-20calculatedthiswaywere:12.7,27.4,29.Thecalculatedgainswerethus:68,93,48whiletheobservedgainswere:66,22,11.

Whythediscrepancy?IthadtobethatthemeasuredQvaluesfor40and20weretoohigh,giventhatthegmwouldnotchangewithfrequencyandthatthecoilvalueswerereasonableandcertainlynotasfaroutasthemeasuredgainswouldsuggest.ItstruckmethatI'dconnectedthesignalgeneratortothegridofthedriver,leavingthecouplinglinktothetunedcircuitintheanodeofthe2ndmixerinplace.Itwaseasytodisconnecttheabove-chassisshieldedcablefromthe2ndmixercolstothedrivergridandfeedthesignalgeneratoronlytothedrivergrid,witha1mHchoketoensureaDCpathfromgridtochassis.

NowthemeasuredQloadedfor80-40-20were:10.4,9.6,6.7.Usingthesevaluesthecalculatedgainswere:57,28,11,muchmoreinkeepingwiththosemeasured.So,I'velearnttoisolateagainstagewhenmakingthesemeasurements.ButwhywastheQlowerthanonewouldexpect,andindeed,byinference,lowerthantheQofthe2ndmixertunedcircuits?Thistookmequiteawhiletofigureout,andtheconclusionisembarrassing!

WhatIshouldhavedonefarearlierwastosketchoutallofthecomponentsthatcomprisetheanodetunedcircuitofthedriver,includingthevalveandscopeparameters.ThisiswhatIendedupdoingandthenusingthatcircuitasthebasisforaMacSPICEsimulation.Thecircuitismorecomplexthanonemightthink,Figure14,andthereisplentyofscopefortheQtobedegradedifthereisunwantedresistanceinanyofthecomponentscontributingtothetunedcircuit.Notehowthe15pFtuningcapacitorisonlyabout25%ofthetotalcapacityacrossthetunedcircuit.Alsonotethatthe470pFHTdecouplingcapacitorandthe91pFfeedthroughdecouplerareinserieswiththefrequency-determiningcapacitors.Therefore,iftherewereexcessivelossresistanceheretheQwouldbelowered.NotethatthecouplingcapacitorfromdriveranodetoPAgridisinserieswiththegrid-cathodecapacitiesofthe6146Bvalves-atotalof27pF.Together,thesecomprisesome50%oftheresonatingcapacitance.Figure14showswhereI'veaddednominal1Ωresistorstorepresentlosses,withthoseincircuit,theMacSPICEsimulationisshowninFigure15(left),whichshowsagainofabout51.MyembarrassingrealisationwasthatI'daddedpreviouslya100 ΩresistorinserieswiththeanodetogridcouplingcapacitortomeasuretheactualPAgridcurrent.Thiswasstillinplace,anditwasnotuntilnowthatIrealisedtheimportanceofthatpathtothedrivertunedcircuitQ.Theeffectofthe100ΩresistorisclearinMacSPICE,Figure15(right)wheretheQhasdroppedsubstantiallyandthegainhasdroppedto15from51.

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Figure14Circuitdiagramofthedriverstagetunedcircuitcomponents.

Figure15MacSPICEsimulationofthedriver-PAresonantcircuitfor14MHzusingthecircuittopologyofFigure12.Left:with1 Ωresistors.Rightwith100ΩinserieswiththePAanode-gridcapacitance. Needlesstosaytheresistorwasremovedforthwith!ThemeasuredQloadedvalueson80-40-20-15werenow:16,24,28,27-farmoreinkeepingwithexpectations.Icouldnotgetthepeakon10higherthan27.4MHzduetotheaddedcapacityofthetestprobe.

Ifoundanew,unused6CL6oneBay(Thomson,MadeinFrance)andwiththisvalve,thepeak-to-peakdriveon80–10attheanodeofthedriverwas:240,274,280,180,120V.Thiswassufficienttoprovide100W(~200Vpeak-to-peak)outputintoa50Wdummyloadon80–20,81Won15and50Won10.

Microphoneamplifierandcathodefollower

With50mVrmsaudiointothefrontpaneljacksocketat500HzthelevelatV1aanode(halfofa12AX7)was2Vrms,againof40.WiththeaudiogaincontrolfullyCWthelevelfromthecathodefollowerV1batthejunctionofR9andR10was0.57Vrms,butdistorted;themaximumlevelatwhichtherewasminimaldistortionwas0.32Vrms.Thevaluesinsection6.4ofthemanualarerathercurious,itcallsfor1Vaudioinputat500Hz,andstatesthat1V

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ACshouldbeseenatthejunctionofR9andR10;1Vinputisfartoohigh,andmymeasurementsshowthatat1Voutputtherewouldbeseveredistortion.

BoththeanodeandcathoderesistorsofV1ahaveincreasedinvalue:R2theanoderesistorfrom100kto115kandR6thecathoderesistorfrom2k2to3k1.TheV1aanodevoltageis181V(cf.160Vinthemanual)andthecathodeis1.66V(1.5Vinthemanual).FromtheECC83characteristiccurves,onewouldexpectahigheranodecurrentatabiasof-1.66V,whichsuggeststheemissionofthisvalveislowerthanwhennew.Consequentlytheobservedgainof40islowerthanthecalculatedgainof~53.

TheV1bcathodeisat1.7V,R8thecathoderesistoris1k14ratherthan1k0;thecomponentsaresotighttothevalvebasethatneithertheanodevoltageortheanoderesistorcanbemeasured.

Themaximumundistortedaudiolevelof0.32VrmsatthejunctionofR9andR10isreachedwithawhistleintothemicrophoneatanaudiogainsettingof12o'clock.However,againsettingofonly9o'clockisneededtoobtainwhistlepeaksofover200mAon80metres.HencedistortionfromtheV1bcathodefollowerisnotanissueinpractice.

435kHzcrystaloscillator

The435kHz"carrier"crystaloscillatoratthefeed-throughpoint"A"inFigure16(Right)was35mVrmswiththeCarrierInsertioncontrolfullyCW.Thefrequencywas435.006kHz;noalternationwasmadetothecarrierPhillipsbeehivetrimmerC60,Figure16(Left).

Figure16Componentlayoutfor(Left)435kHzcrystaloscillator.(Right)partofthecrystalfilterandpartofthe435kHzIFamplifiertoprightwithcarriertestpoint,withCarrierInsertioncontrolfullyCW.

DiodeshuntBalancedModulator

Carriersuppressionwasonlyabout5dBsoonafterswitchon.Whentryingtoadjustthebalancepotentiometerwithascrewdriver,itwasstiff,theshaftsheared!Itwasremovedandreplacedwitha1kΩpotentiometerwithalongplasticshaftthatcouldbeturnedbyhand(R12inFigure17).Thepotentiometerthatwasremovedwassizedsolid,butitwasnottheoriginal;it,andthetwo470Rresistorsateachend,hadbeenreplacedatsometime.ThecapacitivebalanceisadjustedusingC28inFigure17.

Figure18showsthecarriersuppressionatover40dBattheprimarywindingofthebalancedmodulatoroutputtransformer.Theaudiotoneisfroma500Hzinputtothemicrophonesocket.

C60Xtaladj.

“A”Testcarrierxtalfrequencyhere.

IFT2

IFT7

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Crystalfilter-uppersidebandsuppression

ThisViceroycamefittedwiththeextrahalflatticecrystalfilter-thatisfivecrystalsinall,togetherwithaparalleltunedcircuit,IFT7(seeFigure17),whosetuningprimarilyaffectsthe"sag"withinthepassband.

IFT1andIFT2hadbeentunedpreviouslyusingtheprocedureinsection6.5ofthemanual.Now,theRigolDSA815withtrackinggeneratorwasused.Thetrackinggeneratoroutputwasfedviaa50Ωresistortopin6ofthe2xOA79socket.Thespectrumanalyzer50Ωinputcannotbeconnecteddirectlytothefilteroutputandsothecrocclipwasplacedonthebodyoftheunnumbered470kresistoratthegridofV2.Thismeansthatthelevelsarenotright,buttheshapeshouldbecorrect.OnlyslightadjustmentstoIFT1,IFT2andIFT7wereneededtogivethepassbandshowninFigure19.

Figure18Outputofthediodeshuntbalancedmodulator,showingthecarriersuppressionatthispointofabout-44dBforanaudiotoneof500Hzintothemicrophonesocket.

Figure17Componentlayoutoftheaudioamplifier,thebalancedmodulatorandpartofthecrystalfilter.Thecircularscreeningcansonthesub-chassisattherightarethecrystalsfromtheextrahalf-latticesection.

C28R12

IFT7

IFT1

V1

2xOA79inB9Asocket

Figure19Spectrum-span10kHz-showinglowersidebandaftercrystalfilter.Marker1isthecarrierat435kHz,marker2is434.5kHz(500Hzaudio)andmarker3isat432.5kHz(2500Hzaudio).Notethatwithnophysicalconnectiontothecircuitthesignallevelislow.

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Marker2isatanequivalentaudiofrequencyof500HzandMarker3isat2500Hz.Marker1isatthecarrier,about20dBbelowthelevelat500Hz.

VFO

ThefrequencyspanoftheVFOis3065–3665kHz,whichon80mcorrespondsto3500–4100kHzgiventhe435kHzIFcarrieroscillatorfrequency.Theadjustmentat3500kHzisbyinductorL12thathasathreadedrodtowardsthefrontofthechassis.First,onemustslackenslightlythelocknut;onlyslightlyasthecoreisotherwisetooloose.Thecorewasadjustedtobecorrectat3500kHz.At100kHzincrements,theerrorwas0,-3,-3,-1,+3,+2,+1;nofurtheradjustmentwasmade.

Thelevelattheoutputwas1.88Vrms(17.8dBm),themanualcallsfor1.5V.The

close-inspectrumisshowninFigure20,wheretherearespursat+/-1kHzatabout-53dBbelowthepeak.Thesourceoftheseisnotatallclear.TheVFOwaveformattheoutputisshowninFigure21(Left)anditsspectrum(Right).

Figure21(Left)OscilloscopewaveformfortheVFOoutputat3.265MHzat1.88Vrms.(Right)spectrumfrom2–20MHzfortheVFOoutput,withthe2nd,3rdand4thharmonicspresent(relativeonly,notanabsolutemeasurement).

Firstmixer

Thefirstmixer,comprisingthetwotriodeswithinV3(a12AT7),isineffectthesecondbalancedmodulator.ThetwoRFsignalsintothemixercomefrom(a)the435kHzIFamplifierV2viaabalanced"hot"endsofIFT3intothegridsand(b)theVFOintothecentretapofIFT3.BalanceadjustmentisbythepotentiometerR22andthe30pFbeehivetrimmercapacitorC27(Figure22).Toprovidethecorrectsidebandforlateramplification(onthe3.5MHzband),orfrequencytranslation(7,14,21and28MHzbands),inthesecondmixer

Figure20Close-inspectrumoftheVFOoutputatadialfrequencyof3700kHz.Thespanis20kHzandthespursat1kHzfromthecarrierareabout53dBdown.

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theoutputcircuitcomprisingIFT4andIFT6mustbetunedtothesumfrequencyonallbandsexcept7MHzwherethetuningistothedifferencefrequency.

Thefirstprocedure,asdescribedinsection8.3ofthemanual,istoadjusttopandbottomcoresofIFT4andIFT6formaximumsignalwiththebandsetto3.5MHzandtheMixerTuneandVFOfrequenciessetto3700kHz.TheresultisshowninFigure23(left)afterR22andC27wereadjustedtominimisethecomponentattheVFOfrequency(marker2).Disappointingly,thesignalattheVFOfrequencycouldnotbereducedtolessthan20dBbelowthewantedsumsignal.

Figure22Componentlayoutofthefirstmixer.R22isadjustedfromthetopofthechassis.

Withthe7MHzbandselectedthreetrimmercapacitorsareswitchedintothetunedcircuits,110pFcompressiontrimmersC28andC33areconnectedinparallelwiththetwofixedcapacitorsacrosstheprimaryofIFT4andthe110pFcompressiontrimmerC34isconnectedacrossC35theMixerTunefrontpanelcontrol(andtheseriespairofC36andC31).C34islocatedwithinthe2ndMixersub-chassis,Figure26.Figure23(right)showsover45dBofVFOfrequencysuppressioninthiscase.

Figure23Outputofthe2ndbalancedmodulatortakenwiththeDSA815crocclipoverthebodyofC36attachedtotheMixertuningcapacitor.(Left)3.5MHzbandselected,withIFT6tunedtothesum(3700kHz)oftheVFOfrequency(3265kHz)andthe435kHzcrystaloscillator(thisisalsotheconfigurationfor14,21and28MHzbands).(Right)7.0MHzbandisdifferent;IFT6istunedtothedifferencefrequencyof2830kHzinthisexample.I'venotbeenabletofindoutwhytheVFOandsumfrequencysuppressionisbetterinthiscase.

Peakingforthecorrectmixerproductwasquitestraightforwardwiththespectrumanalyzer,butcouldbetrickierusingonlyvalvevoltmeter(asinthemanual)ifthecoresandtrimmers

R22

C27

IFT3

IFT4IFT6

C33 C28

V2

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werewayout.Thesumanddifferenceproductsaresufficientlyfarapartthatmeasurementsoftheperiodonanoscilloscopewouldbesufficienttomakesurethecorrectsignalwasbeingpeaked.Withax100scopeprobethelevelsattheMixerInputtuningcapacitorwere2.6Vrmsatthesumfrequencyof3.7MHzand2.1Vrmsatthedifferencefrequencyof2.83MHzforthe7MHzband.

CrystalOscillatorfortheSecondMixer

Thecrystaloscillator,V12,anEF80,generatestheappropriatefrequenciesforthesecondmixer,V4.Theanodetunedcircuitisabitofacompromiseinthatasingleinductor(L4)isusedwithalowimpedancecouplingwindingtothecathodeofV4.Totunetheprimarytothecorrectfrequency,therearetrimmercapacitorsandacore-tunedinductorforthe10mbandfrequencies.TheTablebelowliststherelevantdetails(frequenciesinkHz),andthelayoutisshowninFigure24.

Band Xtalfreq Holder Mult Adjust OutVrms Tunedfreq Mixer:CO-Input=Output

7 4965 HC6U 2 C76a 4.5 9930 9930-2830=7100

14 6000 HC6U 3 C77 6.6 18000 18000-3700=14300

21 6250 FT243 4 C78 3.6 25000 25000-3700=21300

28a 8025 FT243 4 L10 32100 32100-3700=28400

28b 8175 FT243 4 L10 2 32700 32700-3700=29000

ThemanualstatesthattheinitialadjustmentisthatofL4formaximumoutput(onavalvevoltmeter)atV4cathode(testpoint"A"inFigure26)onthe28MHzband-switchsetting.ThereisnomentioninthehandbookofhowtoadjustL11.Inpracticealigningthisstagewasthemostdifficult,itisquitepossibletotunetheoutputstothewrongharmonics.Thiswasespeciallytrueforthelowerfrequency28MHzband(8025kHzcrystal).Thewanted32100kHzoutputwasdifficulttoachieve,thehighestamplitudeoutputwasat16050kHz,then24075kHz;therewasminimaloutputat32100kHz,evenafterL10wasadjusted,anddifferentcombinationsofL4andL10tuningtried.ThewaveformatFigure25a(left)wasthebestthatcouldbeachieved;the32100kHzcomponentisabout0.5Vrms.Itisnotsurprisingthatthedriveon28MHzisdowncomparedwiththeotherbands.

Thewaveformfortheupper28MHzbandwasbetter,Figure25(centre).Thissuggeststhattheproblemisasluggish8025kHzcrystal.Thiswasconfirmedwhena8050kHzFT243crystalwasinserted,andtheoutputwas2.2Vrms,Figure25a(right).

Figure24Componentlayoutofthecrystaloscillatorforthesecondmixer.

L10.

V12.

L4

C76a

C77C78

7

14

21

28a

28b

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Figure25aOscilloscopetracesfor(left)lower28MHzbandwithoriginal8025kHzcrystal,thewanted32100kHzsignalisweak,(centre)original8175kHzcrystalfortheupper28MHzband,(right)temporarytestwitha8050kHzcrystalshowingadecent2.2Vrms(notethescalehereis20nsperdivisionnot50nsasfortheothertwo).

Later,a8025kHzFT243crystalwasfoundandboughtoneBay,onagamblethatitmightprovemoreactive.Indeedthatwasthecase!Figure25b(leftshowsthespectrumoftheoriginalcrystal(asforFigure25a(left))and(right)thereplacementcrystalshowingabouta10dBhigherlevelatthewanted32.1MHz.

Figure25aSpectrumfrom5–35MHzforthe8025kHzFT243crystalforthelowerpartofthe28MHzbandwherethe4thharmonicat32100kHzisthewantedsignal:(left)originalcrystalwiththetimeseriesshowninFigure25a(left)and(right)areplacementcrystalshowingan11dBhigheroutputat32100kHz.

SecondMixer

Section8.6ofthemanualhastheoutputofthesecondmixermeasuredatthegridofthedriverV5,testpoint"A"inFigure27.Withax100scopeprobeatthistestpoint,andthevariablecapacitorssetasinthemanual,peakingthecoils,Figure26,wasstraightforward.Forthis,IusedtheCarrierInsertiontoprovideasignalratherthananaudiotone.

However,Iswappedtousinga500Hzaudiosignaltothemicrophonesocketat1mVrms,withtheaudiogainfullyCW,tomeasurethesignalatthegridofthedriveroneachband.Thisgivesareferencelevelformetoreturntointhefuture.NotethatwiththeViceroyonStandbyusingtheaudioinputpathrequiresthenegativebiasontheIFamplifierandfirstmixertoberemovedbyshortingthe"valve"sideofR69asperthemanual,section6.2.2,shownaspoint"B"inFigure28.Thevoltagesobtainedareinthetablebelow.

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Band/frequency Drivergrid(V)rms DriverSetting3.7 0.73 7.1 1.1 14.3 3.9 21.3 4.3 at11:30o'clock.NOT2:30

o'clockwhichis25MHz.29.0 5.1 at12:30o'clock.NOT2:30

o'clockwhichis32.7MHz.

MynextstepwastomovethescopeprobetothegridsofthePA,point"A"inFigure28,andtoretunethesecondmixercoilsnowthattherewasnoadditionalloadingatthedrivergrid.

Figure26Componentlayoutofthesecondmixersub-chassis.

3.5.7.

14.21.28

V4.

C39a.

XtalOscin“A”.

C35.

C34.

Figure27Componentlayoutofthedriversub-chassis.

C39b.

3.5.7.

14. 21.

28

V5.

Gridin“A”

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Driver

Section8.7ofthemanualdealswithDriveralignment;usingthegridcurrentmetersettingtopeakthecoilsforeachband,Figure27.Notethatthe28MHzcoilisself-supportingair-coredandisadjustedbysqueezingorexpandingtheturns.Caution!Thiscoilisintheanodecircuit,andsoisatHTpotentialof~260V.Mypracticeistousetwoplasticbladestosetthecoil.

Mypracticewasnowtouseax100scopeprobeofadequateRFvoltageratingatthegridofthePA,testpoint"A"inFigure28.Thisgetsthecoilsforbands3.5–21MHzclosetocorrect,andonecanbesureofpeakingthecorrectfrequency.Notethatthiscannotbedoneforthe28MHzbandastheadjustmentonthecoilisinsufficienttobringthecircuittoresonancewiththeaddedcapacityofthescopeprobe.ThevoltagesonthePAgridfor3.5–21MHzareshowninthetablebelow;notethatwiththebiasat-54Vgridcurrentbeganat37Vrms.

Figure28ComponentlayoutofthePAandVOXsub-chassis.

Band/frequency PAgrid(V)rms3.7 467.1 4914.3 7221.3 63

ALC

InmyearlyinvestigationsonlowdriveI'dthoughttheremighthavebeenanALCproblem,whichIisolatedforthetimebeingbyremovingthe6AL5ALCdoublediodeV13.Nowitwastimetoinvestigate.TheALCcircuitwasthesameinbothofthecircuitdiagramsavailableontheweb,butthereadingofALCoutonthisViceroydidnotmakesensegiventhecircuit:

V6.

V7

PAGrids“A”.

-vebias“B”.

VOXAn8Trip

VOXR28

VOXSensi8vity

RFouttoRelay

RFC750VDC!

R69

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1. OnStandbytheALCoutwasat-27Vinsteadofzero(irrespectiveofthepositionoftheALCpotentiometer-asitshouldbewithnodrive).Thissuggested(a)thatmyALCcircuitmustbedifferent,withanegativefixedbiasonV2inStandby,probablyswitchedoffinCarrierInsertoronanyofthetransmission/tunemodes,asisthebiastothefirstmixerV3and(b)thecircuitaroundthepotentiometermustbedifferentsothatthefixedbiasisnotshortedtoground.

2. OnTune,therewasaDCALCoutvoltagepresentfromjustafewvoltsRFoutputirrespectiveofthesettingofthepotentiometer.

TheALCsub-chassis,Figure29,wasdetachedfromthePAcompartmentandthecircuitworkedout,Figure30,togetherwiththeALCcircuitatthegridofthe435kHzamplifierV2.Thiscircuitmakessenseoftheobservations,butonlyifthe270kresistorfromthe250VHTlinetothepotentiometerwasaveryhighresistanceoropencircuit.Infact,itwasopencircuit.

WiththisarrangementtheALCcontrolvariesthecut-inthresholdfortheALCbyvaryingthepositivestand-offvoltageonthecathodesofthediodes.The"slope"ofthePAanodevoltagetoALCvoltageisfixed.IntheViceroyMKIIIcircuitsonthewebthecut-inthresholdisfixed(as.03oftheHTvoltagebythe220kand6k8resistors),butthe"slope"issetbytheALCcontrol.Ihavesetthepotentiometertogive14Vstand-offvoltage(~0.05oftheHTvoltage).

ThewiringoftheALCpotentiometerissuchthatfullyCCWiswiththewiperat0V,hencemaximumALC,withnostand-off.Thisistheexactoppositeoftheeffectofthecontrolinearliercircuits,wherefullyCCWisnoALC.Thisisanimportantpoint!

ThetablebelowgivestheRFoutputvoltages(rms)attheantennaconnector,witha50Ωdummyload,forfoursettingsoftheALCpotentiometerwiththetransmittersetto"Tune".

Figure30ALCcircuitasinmyMkIVViceroy.

ALCout

220k

220k

1k

1µF

V136AL5

1,5

2,7

1p5

FromPAanodes 250VHT

270k

50k

47k

47kALCin

1M

PartofV2435kHzamplifier

Switched-veBiasin

6.3Vac

250VHT

ALCout

ground

V13

ALCthreshold

Figure29ComponentlayoutoftheALCsub-chassisthatisnormallyscrewedtotheoutsiderearofthePAcompartment.

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VALC Vpot=18 Vpot=14 Vpot=7 Vpot=0

0 30.0 23.0 11.5 0

-0.4 32.4 25.5 12.8 1.6

-1.7 36.5 32.0 18.5 6.8

Performanceagainstspecification

VFOfrequencystability

ThebrochuredescribestheVFOstabilityas"Betterthan100cyclesafterwarm-up".ThemeasurementsinFigure31,takenfromcoldinaroomtemperatureofabout20˚CwithanApolloBlackStar100counter,showadriftto-120Hzfollowedbyariseto+53Hzinthefirst30minutes,followedbyariseinfrequencyof130Hzinthenexthour,levellingofto29,13and0Hzinsubsequenthours.Thisisfollowedbyaslowrise,butnomorethan20Hzperhour.Thisisanexcellentperformanceandmeetsthespecification.

Figure31VFOfrequencystabilitymeasuredwithanApolloBlackStar100frequencycounterbeginningat15:38andendingat22:45on29January2018.

Carrierandunwantedsidebandsuppression

Withtheextrahalf-latticecrystalfilterasfittedtothisViceroythespecificationhasthecarriersuppressionasatleast45dBandtheunwantedsidebandatleast50dBat2kHz.Figure32showsthespectrum+/-5kHzcentredon3700kHzwitha2kHzaudiotoneintothemicrophonesocket,andwiththeanodecurrentonTunesetto100mATheDSA815probewasplacedovertheinsulationofthecoaxcabletotheantennasocket.

Theobservedcarriersuppressionwas-57dBandtheunwantedsidebandat-58dB,bothexceedingthespecification.

3263800

3263850

3263900

3263950

3264000

3264050

3264100

3264150

3264200

3264250

3264300

0 3,600 7,200 10,800 14,400 18,000 21,600 25,200 28,800

VFO

Frequ

ency(H

z)

Timesinceswitch-on(seconds)

VFOdri:

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Spuriousoutputs

TheViceroyspecificationdoesnotcoverspuriousoutputs.ThespectrabelowwereobtainedusingaDSA815withaprobeclipoverthetopoftheinsulationontheinnerconductorofthecoaxialcableattheantennasocket.Thiswilllikelyhaveintroducedafrequency-dependentfactor,butitisasafewaytooperate-thereisalsoa50ohm20dBattenuatoratthefrontendoftheanalyzer.Hencethefiguresdonotrepresentabsoluteamplitudes,butshouldgiveafairindicationofrelativelevels.

80m

Notsurprisingly,the80mbandhastheleastcomplexspectrumofspuriousresponses,Figure33;thisisbecausethereisnofrequencytranslationinthesecondmixer.Point3Risthewantedsignalat3700kHz,withitssecondharmonicatpoint1at7400kHz44.5dBdown,and

thethirdharmonicatpoint3at47dBdown.Point2at435kHzbelowthewantedsignalisattheVFOfrequencyof3265kHzandis42dBdown;thisisfromimperfectbalanceatthefirstmixer.SeeFigure23(left)whereIwasunabletogetabetterVFOsuppressionthan-20dB;theadditional22dBsuppressionseeninFigure33mustcomefromthetunedcircuitsafterthefirstmixer.

Figure32Spectrumof+/-5kHzaround3700kHzwitha2kHzaudiotonetothemicrophonesocket.Marker1isthecarrier,marker2istheunwantedsideband.Notethattherearespursat1and3kHz,butbothareover50dBdown.Theabsolutevaluesarenotrelevant;theconnectionwasbycapacitivepick-up.

Figure33SpectrumoftheViceroyoutputatadialfrequencyof3700kHz,showingsubstantialsecondandthirdharmonicsandtheVFOfrequency.

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40m

On40m,becauseofthesecondmixer,therearemoreunwantedfrequenciespresentthanon80m.Figure34,takenataPAanodecurrentof100mA,hasthewantedoutputat7050kHz,marker1;itssecondharmonic,marker3;andthirdharmonic,marker4.Thepeakjustbelowmarker4,andataboutthesameamplitude,isthefourthharmonicofthesecondmixer4965kHzcrystaloscillatorfor40m,itsthirdharmonicisca.10dBlower,justabovethenoisefloorHFofmarker3,andthesecondharmonicismarker2.

15m

On15mthespectrumhasmoreclose-inpeaksthanon40mwithninespuriiwithin+/-4MHzandtheVFOfrequencyisalsopresent,Figure35.

ItishardtoknowwhetherthesespuriousresponseswerethereintheViceroyfromnew,orwhethersmall

changesinvalveoperatingconditions(e.g.biaspoints,screenvoltages)duetocomponentagingcouldbecontributoryfactorstothispoorperformance.

Figure35SpectrumoftheViceroyoutputatadialfrequencyof21300kHz,ninesignificantsupriiwithin+/-4MHz.

Figure34SpectrumoftheViceroyoutputatadialfrequencyof7050kHz,showingsubstantialsecondandthirdharmonicsandharmonicsofthesecondmixercrystaloscillator.