03-02-2014, 08:40 PM
Don't be afraid to ask questions, its the only way to really learn.
First remember that the RX freq is determined by both the IF freq and the LO freq. Since your IF is now about 20 kHz higher and your LO is still the same, the dial will have to be tuned 20 kHz higher to receive the same station. That's why the osc trimmers need to be readjusted to restore dial calibration.
Use this Nostalgia Air schematic as a reference:
http://www.nostalgiaair.org/PagesByModel...013876.pdf
The drawings show all the alignment points I mentioned. Trimmer 16 is the low freq padder. It is in series with the osc coil and determines the calibration at 600 kHz. The high freq osc trimmer 17 is located on the tuning cap. It sets calibration at 1400 kHz and is in parallel with the tuning cap. When these two freqs are calibrated on the dial, all others should fall into line.
The other two trimmers on the tuning cap are the ant trimmer 4 and the RF (what they call detector) trimmer 5. These are also in parallel with their respective tuning cap sections and are peaked at 1400 kHz for max signal once the osc is adjustments are done.
Trimmer 15 is the first IF primary tuning. Its location on the schematic is confusing because of the combined mixer/osc circuit.
Put your clip lead on the 36 tube so that you can get the osc working enough at 600 kHz to set the low freq dial cal and then take it off for the high freq adjustments.
The Heathkit in the link is the type of inexpensive generator I was suggesting. Just don't pay too much for one. The waveshape is really not too important as the distortion just creates harmonics of the fundamental which are rejected by the radio's tuned circuits. Some of these generators purposely had distorted RF output so that it could generate useful harmonics for alignment at higher freqs.
First remember that the RX freq is determined by both the IF freq and the LO freq. Since your IF is now about 20 kHz higher and your LO is still the same, the dial will have to be tuned 20 kHz higher to receive the same station. That's why the osc trimmers need to be readjusted to restore dial calibration.
Use this Nostalgia Air schematic as a reference:
http://www.nostalgiaair.org/PagesByModel...013876.pdf
The drawings show all the alignment points I mentioned. Trimmer 16 is the low freq padder. It is in series with the osc coil and determines the calibration at 600 kHz. The high freq osc trimmer 17 is located on the tuning cap. It sets calibration at 1400 kHz and is in parallel with the tuning cap. When these two freqs are calibrated on the dial, all others should fall into line.
The other two trimmers on the tuning cap are the ant trimmer 4 and the RF (what they call detector) trimmer 5. These are also in parallel with their respective tuning cap sections and are peaked at 1400 kHz for max signal once the osc is adjustments are done.
Trimmer 15 is the first IF primary tuning. Its location on the schematic is confusing because of the combined mixer/osc circuit.
Put your clip lead on the 36 tube so that you can get the osc working enough at 600 kHz to set the low freq dial cal and then take it off for the high freq adjustments.
The Heathkit in the link is the type of inexpensive generator I was suggesting. Just don't pay too much for one. The waveshape is really not too important as the distortion just creates harmonics of the fundamental which are rejected by the radio's tuned circuits. Some of these generators purposely had distorted RF output so that it could generate useful harmonics for alignment at higher freqs.
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