Hello everyone!
I have at home two old USSR radios VEF 202. One is from a friend and the other one from a neighbour.
The first one works very fine on every band now and I replaced the contacts from the battery case too and the electrolityc capacitors.
The second works, but it makes a bad noise on the low part of the long waves a strong whistle and also the same whistle is appearing while receiving any station on medium waves. Also, the local station sounds distorted and sometimes even during the night the same problem happens to the other stations. When I tested the audio amplifier as an auxiliar, the sound is good. Where should I look for the problem?
P.S: At this radio I haven't replaced any capacitor yet.. but I don't know exactly if the cause of whistle is this.
VEF 202 from Andrei Daniel Lazarescu on Vimeo
Here is the diagram:
I have at home two old USSR radios VEF 202. One is from a friend and the other one from a neighbour.
The first one works very fine on every band now and I replaced the contacts from the battery case too and the electrolityc capacitors.
The second works, but it makes a bad noise on the low part of the long waves a strong whistle and also the same whistle is appearing while receiving any station on medium waves. Also, the local station sounds distorted and sometimes even during the night the same problem happens to the other stations. When I tested the audio amplifier as an auxiliar, the sound is good. Where should I look for the problem?
P.S: At this radio I haven't replaced any capacitor yet.. but I don't know exactly if the cause of whistle is this.
VEF 202 from Andrei Daniel Lazarescu on Vimeo
Here is the diagram:
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Sounds like modulation noise , this can be attributed to many causes like IF instability due to failure of IF bypass capacitors, excessive gain of IF stage due to failure of the IF bias resistor/capacitor , misaligned IF transformers ( peaked too sharpish ) there is a lot more........ including the IF wavetrap and bad image rejection .
Thats just the start.
Start by concentrating on the IF section .
Thats just the start.
Start by concentrating on the IF section .