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President McKinley EU Unlocked Clarifier


Active Member
Oct 26, 2011
Does anyone have an idea about unlocking the clarifier on the European model President McKinley?
The board is much different than its USA counterpart.


Well-Known Member
Jan 29, 2006
If you can share a schematic, I can give you the components to change.

If not, all "regular" clarifiers work basically the same. The external single Clarifier knob (not a split Coarse/fine) has RX only voltage going to it. Trace the middle (wiper) connection output and at some point, it will go through a diode. After the diode, you should see another diode connecting to the same circuit. That diode is from the TX only voltage circuit and it should come from a variable resistor.

To "unlock" the clarifier, you need to disconnect the diode on the TX only circuit and replace the RX only voltage on the external Clarifier with the same constant voltage.

Many external clarifier's, on the low side, go to ground through a resistor. For example, the 148GTL goes through a 3.3K to ground. Replace the fixed resistor with a variable that is ~2x larger - in that case a 5K (10 turn precision is best).

After making the changes, finish up by setting the clarifier to the 12:00 o'clock position and adjust the variable resistor going to ground to "align" the frequency.

This way you don't have to adjust any of the coils or anything else - you can zero beat it on TX or RX. Jut make sure your constant voltage source doesn't change by more than .02v between RX and TX.


Well-Known Member
Jan 29, 2006
Remove RT303 - this will disconnect the TX only voltage


Remove R347 - this will remove the RX only voltage from the high side of the clarifier.


Connect the constant 8v on the right side of R320 (not Q306 side). Any point on the schematic marked "V8" will work. Do not use any point marked "VR8" or "VT8" for your voltage source.


To the vacant right pad of where R347 was (connects to the left/end wire of J409).



To align, put clarifier at 12:00 and adjust RT304 to get on Freq.



Easy Peasy. I also attached the service manual for it.

Good Luck.


  • service-manuals_service-manual-mc-kinley-eu-gd-13-06-2019.pdf
    12 MB · Views: 6

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