Heath HR-10 Modifications - Nostalgic Kits Central

Wayne Montague VE3FYL1190 Atwater AvenuePort Credit, OntarioCanadaHeath HR-I0 ModificationsThe lIeath IIR-lO receiver is an excellentchoice for the novice, but with our crowdedbands these days, improving the selectivityof any receiver is a worthwhile project.The modifications described here include increasedselectivity and sensitivity and makethe set act as if it cost much more than thetotal outlay for the circuit changes-a meretwelve dollars.Since the IIR-IO appears to be a verypopular receiver with novices and generalsalike, these modifications will be for themutual benefit of all. In addition to the sensitivityand selectivity improvements, I addedvoltage regulation, rearrangedcontrol. put in a new S-meteradded a solid-state rectifier.the rfcircuit.gainandIn the front-end 1 replaced the 6BZ6 rfamplifier with a 6AK5. Before installing the6AK5, remove the I20k screen-grid resistorfrom the circuit and lift pin 7 of the tubesocket from ground. The increased sensitivityis well worth this simple modification.To improve the stability for SSB and CWoperation, 1 added a voltage-regulator tube.I used an OA2 because I happened to haveit in the junk box, but an OB2 should workjust as well. Since the 6X4 rectifier is re-* "",6E.l.8MIJC£R, ,-- ,J~'r,II*fiRST IF'" *6BA6 ...,•~.k•"..SEOONO IF~I~~E~TN~FWIRING LEfT INTACT)S- METER•ec .. *."""o••CAI. . RfSfT,.~ .,* • ~2 OR 082 1"1, ..:,:..' 6X4 SOCKE T (LL /lVE•'"su, • G>fJ ~ .~""TO 8+1lF0 OlOl/OfFO~-lTO 6EA8 111' 1 •8F'O (68k ON TERM.sr_,e'"~,Modified HR · l0 circuitry. These changes result in improved se nsitivity, selectivity and stability.86 • 73 MAGAZINE

placed by two 500 mA, 600 PIV silicondiodes, the 6X4 socket is used for the VRtube. In addition, you will need some additionalsolder lugs. This can be accomplishedby installing a 3-lug terminal strip in placeof the 2-lug strip which is mounted nearthe BEA8 in the mixer section.In this modification most of the harnesscab le can be rewired and rerouted to thenew point, saving wire and preserving overallneatness. To install the new S-meter(Lafayette 99R2514), remove the pilot lightin the left-hand corner, remove the old S­meter and the black metal bracket and cut a2 J ~ " hole through the front panel. Cut thehole so th e old S-meter calibration pointsare removed in the waste plastic.AlignmentThe HR- IO in its modified form is a verysensitive receiver, and since we are squeezingthe last bit of performance out of it, thealignment of the various stages is a littlepainstaking. The first step is the alignmentof the if stages. If you have a signal generator,all well and good. If not, use a heatnote from the crystal calibrator. For properselectivity the if transformer slugs are set forthe first peak after the slugs are screwed allthe way out and back in again.If you encounter oscillation in the ifstages, it can be cured by lowering the valueof the 6IlA6 grid resistor, slightly detuningthe second or third if or shunting the secondif transformer with a 68k resistor. After youare satisfied that the if stages are properlyaligned, proceed with the alignment of therf stages.ResultsAfter these simple modifications, the setworks like a charm. In fact, it is too selectivefor AM work, but just dandy for CW andSSn. In addition, frequency stab ility is excellent,and it takes a pretty large fluctuationin line voltage to make it jump off frequency.Setting the rf gain control has no bearingon S-meter position-it just decreasessensitivity, lowering the reading, but not pinningit up scale. I find that on forty metersI seldom have the rf gain control much abovethe one o'clock position.I would like to thank Ted, VE3ABN fortyping, and John VE3FWX, for his constructivecriticism.. • . VE3FYLJULY /967Luxury with Ecol1omy1" Euhionable Murray Hil/,N ew Y ork CityNo New York City parking problems ­just drive up to.our door and let us take- care of your car.The ROGER WILLIAM S HOTEL issa conveniemly located to most of the city's exciting attranians;induding Times Square, Radio City, Lincoln Center, EmpireStare Building, etc. The ROGER WILLIAMS HOTEL ctlersa homdike atmosphere in bcauriful rooms with moderntelevision, Air ron ditioninJ:, and a good Restaurant andCo!f.e(' Shop, W rite for folder DB2Phone: ( 8 1 B j, MUe·OeOOROGER 'W"ILLIA lo4S H OTELMADI SON AVE. a t 3 1at STREETNJ ~'0fY! W"CIDIR\]KMORE TALK POWERWITHOUT DISTORTIONSPEECH COMPRESSOR CSPI IA New and novel desig n provides lnstenteneouspe ek lirnitinq with no distortion. Theunit installs in microphone leeds and providesan effective average power gain of 10 d Brelative to the peak output. Its usefu lnessepplies to all forms of voice t ransmissionsincluding and especially sing le sldebend.Pri ce: $111.00 Postpaidin U.S.A.(Add 3% Tax in Moss.)WrIte For free Brochur.COMDEL, INC.218 Bay Rd ., Hamilton, Ma n . 01 98287