The President Lincoln radio uses a rotary encoder. Although this radio is very reliable, years of use can take their toll, and problems may arise with the encoder. The easiest solution is to replace it with a new encoder.
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Inexpensive Rotary Encoder—Tuning Knob
Since the original type is hard to find, I tried the KY-040 rotary encoder, which is used as a sensor for devices like the Arduino. It has 20 pulses per revolution and also includes a button.
The original encoder has 3 wires; the KY-040 has 5. The encoder connection is shown in the photo: the purple wire to GND, the gray wire to CLK, and the white wire to DT. The auxiliary resistors on the circuit board remain; no changes are made to the wiring.
Installing the Encoder into the Radio
The photo shows the unit still in the testing phase. For a stable installation, I recommend soldering the wires directly to the circuit board. The KY-040 rotary encoder can fit into the space where the original encoder was located, but it needs to be centered because the shaft diameter is smaller. You can use heat-shrink tubing or another method, for example.
Improvement Options
For experimenters, there is also the option of using the switch in the encoder, for example, for the SPAN button. This would allow the step to be selected directly from the tuning knob, but to do so, the KY-040 would likely need to be modified, since the button, according to the President Lincoln radio schematic, is not connected to GND, as it is on the KY-040 circuit board. You can find inspiration for this modification at http://mm1ewa.blogspot.com/2011/05/uniden-2830-vfo-mod.html
The replacement is not difficult, but it does require loosening four screws and removing the front panel; however, access to the encoder is limited.