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grundig: Cause of High Voltage

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Forum » Radios and other type of sets (Physics) etc. » MODELS DISPLAYED » grundig: Cause of High Voltage
           
Craig Vodnik
Craig Vodnik
 
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23.Sep.17 22:30

Count of Thanks: 5
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I've recapped my console by reading the values from the old caps and replacing with the appropriate modern version.  

In all of the restorations that I've done, I've never seen a Grundig schematic that has a voltage listed on greater than 300V following the rectifier so when I measured 330V, I tried to check things to see what the possible issue was.

I replaced the rectifier and measured 270V at the DC output side with nothing connected to it.  As soon as I reconnected the rest of the electronics to the DC output side, the voltage jumps back to 330V.  

I have replaced a number of the tubes, but since I don't have the schematics, I am struggling to figure out where the problem is.  Any guidance of what to look at it appreciated!

craig.

Tomasz Szczesniak
 
 
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23.Sep.17 23:20

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It is normal behaviour. Bare rectifier (without capacitors) has DC at output at mean value. When capacitor is added DC value equals to amplitude of AC voltage connected to rectifier. When capactor and some load is connected the DC value is lower than amplitude, but still higher than this without any other elements connected to rectifier.

Craig Vodnik
Craig Vodnik
 
USA  Articles: 48
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Pict.: 34
30.Sep.17 23:49

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Thanks Tomasz. Put a wirewound resistor in between the rectifier and main electrolytic caps, voltage went to expected level.

Now I'm experiencing no sound output at all even though the voltage is where it should be.  I'm sure that it's something simple because before I reduced the voltage, I could get some (garbage) audio out of the speakers.  Any thoughts on what and how to test for this issue?

  
rmXorg