BLACK BOX MODS FROM JACK PLUG THE BLACK BOX CHARGE INHIBIT CIRCUIT CURRENTLY CIRCULATING AGAIN (6.1K RESISTOR, LED, CAPACITOR, DIODE, ETC) SEEMS NOT TO WORK ON SEVERAL SYSTEMS. A USEFUL MOD IS TO REPLACE THE EXISTING RESISTOR WITH A VARIABLE TYPE. CHOOSE EITHER A 0 TO 10K OR A 0 TO 1K VALUE TYPE AS MANY INSTRUMENTS CAN BE "BALANCED" WITH QUITE LOW ADDITIONAL RESISTANCES. TRIMMERS OR PRESETS ARE THE CHEAPEST, BUT FOR EASY AND ACCURATE READJUSTMENT GO FOR THE MULTI-TURN CERMIT TYPE OR SIMILAR. TO SET-UP, INSTALL THE BLACK BOX AND SET THE RESISTOR TO ITS LOWEST VALUE POSITION (FULLY ANTI-CLOCKWISE). WITH THE BOX OFF, LIFT THE HANDSET AND CHECK FOR A DIALLING TONE. NOW SWITCH THE BOX "ON" AND CHECK THAT THE TONE REMAINS. THE NEXT STEP IS TO GRADUALLY INCREASE THE RESISTANCE, CHECK FOR THE DIAL TONE, INCREASE THE RESISTANCE, CHECK FOR THE TONE.... AND SO ON UNTIL A POINT IS REACHED WHERE THE DIAL TONE EITHER FLUTTERS OR DISAPPEARS COMPLETELY. AT THIS POINT DECREASE THE RESISTANCE S L I G H T L Y. WITH A VOLMETER CONNECTED IN PARALLEL ACROSS THE LINE YOU SHOULD NOTICE THE USUAL VOLTAGE DROP WHEN THE HANDSET IS LIFTED AND THE BLACK BOX OFF. wITH THE BLACK BOX ON, HOWEVER, THE OFF-HOOK VOLTAGE DROP SHOULD BE CONSIDERABLY LESS. IN USE, THE BOX SHOULD BE SWITCHED ON WHEN SOMEONE RINGS YOU OR WHEN YOU HEAR THE RINGING TONE OF THE PERSON YOU ARE CALLING. IF THERE IS ANY JUSTICE, WHEN THE BOX IS SWITCHED ON THE EXCHANGE METER WILL "SEE" THE VOLTAGE SWING ASSOCIATED WITH YOU REPLACING THE HANDSET AND STOP COUNTING. ENOUGH CURRENT REMAINS, HOWEVER, TO FIRE-UP THE MIC AND FACILITATE CONTINUANCE OF THE CONVERSATION. SOME ODD THINGS HAVE HAPPENED WHILST WATCHING OTHERS USE THIS DEVICE (!). AT ONE POINT, THE BOX SWITCH WAS CLICKED OFF AND ON QUICKLY DURING A CONVERSATION AND A DIGITISED VOICE ANNOUNCED THAT "RECALL IS NOT AVAILABLE, YOU WILL BE RECONNECTED TO THE CALLER," AND THE CREDIT DISPLAY IN THE PHONE BOX THAT HAD INITIATED THE CALL PROMPTLY STOPPED CLOCKING DOWN. I HOPE THIS IS OF USE TO SOMEONE. REGARDS: JACK PLUG. (BY THE WAY, I HAVE FOR SALE OR SWAP A "MOULD" SELCALL UNIT. FULLY OPERATIONAL WITH INTACT EPROM/CALLSIGN. WANT VERY CHEAP TNC OR RTTY INTERFACE. DESPERATELY NEED CIRCUITS/INFO ON "TEMPEST.")