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Timo Haveri
FIN Articles: 9 Schem.: 0 Pict.: 28 16.Jun.08 23:19 |
stern-sonn: 697/75GWU 3D; Sekretär III
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I'm restoring a Sekretär III 697/75GWU 3D radio. There wasn't a schematic for this model in RMorg but I used a schematic for model Sekretär III 697/62GWU which I believe to be close enough. There are no component values in the schematic and I need to know the value of one resistor. It is burned open and the markings are no longer visible. I think it is R11 in the schematic (in the lower left corner, antenna circuit). I have no idea how it got burned. There is no visible damage in the other components. Also I removed the 50 + 100 uF electrolytic capacitor can but I forgot to look which one is the first and which one is the second filter. I'm guessing that the 100 uF is the first. Am I right? The final question is about the half wave selenium rectifier. I measured its resistance with a digital ohm meter and I got 1.3 megaohms in the other direction and 1.6 megaohms in the other. I assume that it is bad? All answers will be greatly appreciated. Timo |
Martin Renz
D Articles: 323 Schem.: 96 Pict.: 106 17.Jun.08 15:56 |
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Hello Timo, you can use the schematic of the 697/77 GWU Sekretär 4 modell. The component values are added there. You can't check a selenium rectifier with a digital ohm meter. Check the anode voltages instead. If they all are too low, or the rectifier gets hot, this indicates a possibly bad rectifier. For more information look here and may be here and here (about restauration in general by Hans Knoll) This article was edited 17.Jun.08 18:44 by Martin Renz . |
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Timo Haveri
FIN Articles: 9 Schem.: 0 Pict.: 28 17.Jun.08 20:46 |
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Thank you Martin. I have checked selenium bridge rectifiers before with a digital meter and they behaved just like normal diodes. None of them showed reverse leakage but this one does. I'll try carefully how the original rectifier performs. I already tried the radio with a silicon diode + resistor and it worked but quite weakly. It seems that the volume potentiometer has some problems. And it needs a new UM80 eye tube. Maybe some other tube is also bad. Timo |
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