12-08-2021, 10:42 AM
Chris, it appears that the squeal could be caused by an oscillation in either the RF or IF amp stages. Does the squeal occur as you tune through a signal on all bands or only on broadcast? Uniformly on a band or only in certain parts of the dial?
If it is selective on only some bands or ranges of tuning, then it is most likely caused by the RF stage. If it happens on all bands and uniformly across the dial then its probably in the IF. Some cheap shortwave receivers actually made the IF amp oscillate on purpose to provide a beat oscillator function for CW reception.
Typically an oscillation like this is caused by a bad ground or open screen grid, cathode or B+ supply bypass cap. You can try jumping a known good .05 uf cap across each bypass and see if it cures the squeal.
If it is selective on only some bands or ranges of tuning, then it is most likely caused by the RF stage. If it happens on all bands and uniformly across the dial then its probably in the IF. Some cheap shortwave receivers actually made the IF amp oscillate on purpose to provide a beat oscillator function for CW reception.
Typically an oscillation like this is caused by a bad ground or open screen grid, cathode or B+ supply bypass cap. You can try jumping a known good .05 uf cap across each bypass and see if it cures the squeal.
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