RCI 6900F TB ALC Mod, Tune-Up, And PCB Adjustment Locations by Bob F

The ALC modification requires the removal of surface mount parts and the addition of conventional through hole type parts. When removing these components, take extra care not to overheat the circuit board. The traces will lift quite easily. When installing standard components, due to their larger size, it's best to solder them to the trace where another component is already soldered. This will be a stronger connection as these larger components will vibrate and pull the traces up in time. If you're not sure about what your capabilities are, don't attempt this modification. Take the mod to a local technician or send in to Bob's CB & Wireless.


RCI-6900F TB Sideband ALC Modification
  1. Change R259 from 470 Ohm to 10K (See Figure 1)

  2. Change R271 from 1K to 2.2K (See Figure 2)

  3. Add two 1N4148 diodes in series across R217 band side to ground. (See Figure 2)

The following adjustments require the front panel RF Power Control to be set to the fully clockwise position. To adjust the SSB power, set VR18 SSB Limit to maximum and adjust VR14 up to 150-Watts PEP. This will produce a clear SSB signal from minimum power to maximum power. For AM, Set VR15 to 50 to 70-Watts and adjust VR17 for a modulation swing of 150-Watts peak. Remember; the front panel control will allow the RF carrier output to be reduced at will. If you don't want much swing at low power, unfortunately the modulation adjustment will have to be reduced, and a 150-Watt peak at high power won't be possible.

Figure 1


Figure 2


RCI-6900F TB PC Board Adjustment Locations
VR1 - AM/FM "S" Meter Adjustment VR11 - Final Bias Adjustment
VR2 - SSB "S" Meter Adjustment VR12 - Final Bias Adjustment
VR3 - SSB Coarse Squelch Adjustment VR13 - Driver Bias Adjustment
VR4 - AM/FM Coarse Squelch Adjustment VR14 - SSB Power Adjustment
VR7 - FM Deviation Adjustment VR15 - AM/FM High Power Adjustment
VR8 - Transmit Frequency Adjustment VR17 - AM Modulation Adjustment
VR9 - CW Power Adjustment VR18 - SSB Limit Adjustment
VR10 - RF Meter Adjustment VR19 - Low Power Adjustment

Bob F

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