03-17-2022, 10:29 AM
Considering how the oscillator circuit is designed, the trimmer labeled 19A which is connected to switch pins A5,A6 would be the LF padder adjustment at 580 kc. It typically has a set capacitance of about 700 pF, which is right in the range of the 350 to 900 you measured.
The other section of the trimmer 19 connected to switch pin A2, is the HF adjustment at 1400 kc. It should have a much smaller capacitance as it is effectively in parallel with the tuning cap in broadcast band position and should have a significant effect only at the high end of the band.
When you measured the capacitance of the trimmer, did you measure both sections and did the readings differ?
Given there is some error in the labeling of trimmers 19 and 19A it may be confusing as to which is which. In any case, the trimmer section measuring 350 to 900 pF should be connected to A5, A6 and pin 4 of the coil, and should be the 580 kc adjustment.
The other section of the trimmer 19 connected to switch pin A2, is the HF adjustment at 1400 kc. It should have a much smaller capacitance as it is effectively in parallel with the tuning cap in broadcast band position and should have a significant effect only at the high end of the band.
When you measured the capacitance of the trimmer, did you measure both sections and did the readings differ?
Given there is some error in the labeling of trimmers 19 and 19A it may be confusing as to which is which. In any case, the trimmer section measuring 350 to 900 pF should be connected to A5, A6 and pin 4 of the coil, and should be the 580 kc adjustment.
