An old friend of mine radio brought me his old radio asking for its restoration, since it has the power cord which was cut. The radio, a Magnadyne FM 12 which dates back to year 1955, manufactured from the well-known Italian maker from Turin, looked in good conditions, without rust on the chassis, only with some minor wear on the wooden case. After giving it a dusting and a general cleanup, the device looked nearly as new.
After having replaced mains power cable and verified that there were no evident scorch marks, I tried to start the radio up with lower voltage for about half an hour. After this, I power it up at normal voltage and the radio started to work reasonably well.
In a few minutes of operation, however, the radio started to sound with some distortion, together with overheating of the power output tube, symptom of the usual fault of the audio decoupling capacitor between the pre-amplifier and the power tubes. After replacing the capacitor, the radio was playing great again.
Nearly convinced to put the chassis back in the radio, I power it up for a last test, but I realized that the radio wasn’t able to work in frequency modulation. I checked the area of the FM section, which is located in a separate area, above the variable capacitor (this one is for AM wave bands only): the dial string entering the FM section was loose. FM group in this radio is variable permeability tuned, that is the inductance of the antenna and oscillator varies, and the cord allows the sliding of the magnetic core of the respective coils.
After opening the FM group, it was evident that the cord was broken near the spring which keep the string in tension. In order to fix it, I replaced the string and restore the correct tension, in order to match the received frequency with the one of the tuning dial.