Heath SB-610 Monitor Scope Modifications - Nostalgic Kits Central

that I also use when mobile, this wouldinvolve additional connections to attach andremove each time I switched from b ase stationto mobile operation. Xly modification accomplishesthe clamping of the trace withno additional connections to the transmitteror receiver.Parts required:Capacitor, .05 rnfd, 50 voltsHesistors: 33K, ~ watt and resistor inseries with relay coil (see text)Sensitive plate relay, DPST, N.O., (LafayetteRadio 99H6093, DPDT, 5300 ohm,4.1 mn., 4 oz., shipping weight, $2.95,Lafayette Haclio, 11 1 Jericho Turnpike,Syosset, L.T. , N.Y. 11791 ) Sec text fordetails.The relay I used, was from my junkbox. Lacking a suitab le relay, the one listedin the list above is suggested. It may require ingenuity to mount some relays, buta small bit of epoxy will do wonders ifproperly applied.Fig. 4 shows the circuit modifica tions tobe made. The dark portions of the circuitare addi tional components or modifications.The clamp tube, VlB, is turned into a relayamplifier. Relay contacts are used to pullthe trace off the screen by shorting thehorizontal position control through a 33 Kresistor. A second set of contacts groundsthe grid of V3A to stop the sweep. If thesweep is not disabled, the left portion ofthe trace will still be on the screen. Pins 1and 2 of the front panel sweep control arejumpered so that the "pull for clamp" controlwill work in the internal sweep positionof the sweep control as well as in the othersweep positions. When this modification ismade, the SH-6IO will operate as originallydesigned in the RTTY and rf Trap positionsof the sweep switch. T he clamp will a lsowork in the internal (In t.) position of thesweep control when the "pull for clamp" controlis pulled out. The d amp switch mayhe pushed in so that received signals mayalso be monitored as originally designed.The .2 microfarad capacitor on terminalstrip H adjacent to tube socket VI ischanged to .05 microfarads to allow 1 to2 seconds before the trace leaves the screen.This capacitor need not be changed, hut thetime for the trace to leave the screen willbe in excess of ten seconds if it is notchanged. Remove the capacitor from stripH and replace it with the .05 mfd capacitorif you desire this change.44•Bottom ViewThe left hand lug of terminal strip U,near the chassis edge was originally unused.Remove the blue wire at pin 7 of VI andsolder it to this unused lug of terminalstrip U. On the back of the front panel,solder a jumper wire between lugs 1 and" of the sweep switch.Mount the plate relay in the space betweenthe tube socket VI, terminal stripU and the edge of the chassis. If your relaycan he mounted with screws as could myjunk box relay, that is fine; otherwise youmay have to use some ingenuity and p erhapssome epoxy to mount the relay.F rom one set of relay contacts (closedwhen the relay is operated) nm a wire to aconvenient ground point such as the mountinglug of terminal strip U. From the othercontact of the set, connect the 33 K resistorto the blue wire which you soldered to thepreviously unused lug of terminal strip Uncar the outside of the chassis.From the second set of contacts (alsoclosed when the relay is operated) run awire to ground. From the other contact ofthis set. run a wire to pin 9 of tube socketV3A which is the tube socket ncar the shaftextension. This set of contacts will nowground the grid of tube V3A when therelay is closed and stop the sweep.Run a wire from one end of the relaycoil to the 280 volt bus. I ran the wireto the junction of the 40 mfd capacitor;is K, 1 \V resistor; 1 K, J \V resistor;and 20 mfd capacitor. This is ncar the centerof the chassis on capacitor K, pin 3.Temporarily, attach the remaining endof the relay coil to pin 7 of VI througha resistor. (This resistor sho uld he nominally]5 K ohms for the relay in the parts list.)The resistor should be selected so that therelay used just pulls in reliably when the73 MAGAZINE