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555rfgain [2007/04/30 15:56]
n5na created
555rfgain [2007/05/20 20:42] (current)
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   -Note: Connectors 26 and 27 in the extreme corner of the board between the Mic Gain/RIT pot and the PTO will be left open.   -Note: Connectors 26 and 27 in the extreme corner of the board between the Mic Gain/RIT pot and the PTO will be left open.
   -While you have the Scout open, perform the following modification. Locate the blue S-meter lamp wires, cut one and install a 56 ohm resistor in series with it. Use sleeving to insulate the resistor leads. Temporarily unplug the lamp from the meter housing, if necessary. This change will greatly reduce night time glare from the meter and will extend the life of the lamp.   -While you have the Scout open, perform the following modification. Locate the blue S-meter lamp wires, cut one and install a 56 ohm resistor in series with it. Use sleeving to insulate the resistor leads. Temporarily unplug the lamp from the meter housing, if necessary. This change will greatly reduce night time glare from the meter and will extend the life of the lamp.
-  -Turn the transceiver over and unplug connector 41 from the Low Level Driver board. Remove the FWD/SWR switch from the rear panel. Remove the switch leads from connector 41 and install a jumper on the connector to select the SWR meter function. Plug connector 41 +  -Turn the transceiver over and unplug connector 41 from the Low Level Driver board. Remove the FWD/SWR switch from the rear panel. Remove the switch leads from connector 41 and install a jumper on the connector to select the SWR meter function. Plug connector 41 back into the Low Level Driver board. 
-back into the Low Level Driver board. +    *Note: The new mic gain control will be installed in place of the FWD/SWR switch. Use a miniature 10 k ohm potentiometer. If you want to retain this switch, consider mounting a miniature trim pot for mic gain inside the Scout. I find that the mic gain seldom needs to be adjusted (never if  you only run CW!), so mounting the control internally, with or without an access hole in the bottom ​ cover is a reasonable alternative.
-  *Note: The new mic gain control will be installed in place of the FWD/SWR switch. Use a miniature 10 k ohm potentiometer. If you want to retain this switch, consider mounting a miniature trim pot for mic gain inside the Scout. I find that the mic gain seldom needs to be adjusted (never if  you only run CW!), so mounting the control internally, with or without an access hole in the bottom ​ cover is a reasonable alternative.+
   -After choosing a location for the new mic gain control, route the 2 shielded cables installed in steps 10 and 11 to the chosen location.   -After choosing a location for the new mic gain control, route the 2 shielded cables installed in steps 10 and 11 to the chosen location.
   -Reinstall the speaker/​display mounting plate.   -Reinstall the speaker/​display mounting plate.
-  -Connect the shield wires to the low side of the new control. Connect the center conductor of the cable from  connector 26 to the wiper and connect the center conductor from connector 27 to the high side of the pot. I put ferrite beads on the center conductors +  -Connect the shield wires to the low side of the new control. Connect the center conductor of the cable from  connector 26 to the wiper and connect the center conductor from connector 27 to the high side of the pot. I put ferrite beads on the center conductors where they solder to the pot, but again, this may not be necessary. Mount the pot in the chosen location.
-where they solder to the pot, but again, this may not be necessary. Mount the pot in the chosen location.+
   -Turn the Scout over to expose the foil side of the I.F./Audio board.   -Turn the Scout over to expose the foil side of the I.F./Audio board.
   -Locate terminals 26 and 27 in the notched-out corner of the I.F./Audio board, adjacent to the Tune/NB switch. With an ohmmeter, determine which terminals connect to the front panel mic gain control, which will become the new R.F. gain control.   -Locate terminals 26 and 27 in the notched-out corner of the I.F./Audio board, adjacent to the Tune/NB switch. With an ohmmeter, determine which terminals connect to the front panel mic gain control, which will become the new R.F. gain control.
-  ​*Note: Use sleeving on the diode and resistor leads in the following steps. You will be working on the foil side of the board. It is not necessary to remove the board.+    ​*Note: Use sleeving on the diode and resistor leads in the following steps. You will be working on the foil side of the board. It is not necessary to remove the board.
   -Connect a 3300 ohm resistor from the low side of the R.F. gain pot to the ground foil near the circuit board mounting screw. Connect an 820 ohm resistor from the high side of the pot to the +13 V "​R"​ (Receive) voltage at connector 9, at the opposite edge of the board. Connector 9 has the "​R"​ and "​T"​ voltages (see schematic). The "​R"​ voltage is the thinner circuit trace.   -Connect a 3300 ohm resistor from the low side of the R.F. gain pot to the ground foil near the circuit board mounting screw. Connect an 820 ohm resistor from the high side of the pot to the +13 V "​R"​ (Receive) voltage at connector 9, at the opposite edge of the board. Connector 9 has the "​R"​ and "​T"​ voltages (see schematic). The "​R"​ voltage is the thinner circuit trace.
   -Connect the pot wiper to the anode of a 1N914 or 1N4148 diode. Connect the cathode of the diode to Q5-emitter.   -Connect the pot wiper to the anode of a 1N914 or 1N4148 diode. Connect the cathode of the diode to Q5-emitter.

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