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 Post subject: Which Bridge should I order?
PostPosted: Feb Sat 05, 2011 3:10 pm 
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Location: Fredericton, Canada
Hi: I am looking for advice on which bridge I should order for my Blaupunkt radio. The selenium bridge in it now is the usual type in these radios ( marked 250/50). I have the Digi-key catalog and am looking at part number 36MB100A-ND. It has a 1000 Volt peak inverse voltage. Is that too high or should I go higher? thanks for any advice

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 Post subject:
PostPosted: Feb Sat 05, 2011 3:20 pm 
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Bridge rectifier, I assume....

What is the voltage in the set? Is this for the output of the transformer to rectify the B+? If in doubt, please post the model number and/or a link to the schematic.

A diode rated at 1000volts would be fine for almost radio on the planet. There's no penalty for going higher, and there's no money to be saved by going lower. I guess that's why there are so many 1N4007s


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 Post subject:
PostPosted: Feb Sat 05, 2011 3:21 pm 
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Are you sure you need a bridge and not just two diodes? Anyway, your 1000V PIV diodes should work fine; it's very unlikely you are even coming close to 1000v PIV in the circuit unless there's a hidden transmitter somewhere in it.

Pete


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 Post subject:
PostPosted: Feb Sat 05, 2011 3:25 pm 
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The original appears to be marked as 250 volts and 50 ma. I think the 1000 volt replacement would be a good choice.

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 Post subject:
PostPosted: Feb Sat 05, 2011 3:30 pm 
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Joined: Nov Sun 08, 2009 9:48 pm
Posts: 330
Location: Fredericton, Canada
Sorry for not being clearer. This is a four diode selenium bridge which rectifies the power transformer output to provide B+. The model is a Blaupunkt Riviera 2540. One correction on my part- The schematic labels the bridge rectifier B250 C100. The two pi filters are 100uf. B+ is marked at 272 Volts at the bridge output. I could use four IN4007 diodes to make a bridge but a single package would look neater. I just want to make sure the bridge is within specs.

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 Post subject:
PostPosted: Feb Sat 05, 2011 4:31 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Cortez, Colorado
I've seen the flat pack bridge rectifiers in German radios that are about 2 1/2" X 1 1/2" X 3/8" and the round about 5/8" X 3 to 5". In the flat packs, after gutting them, I have installed 4 1N4007s and a 20-50 ohm resistor external. In the round ones I install a Fairchild 1.5 amp 1000PIV round bridge, with a resistor inside. Mouser has them in Vishay http://www.mouser.com/ProductDetail/Vis ... PjeI5E4Rr5

I have a Riviera that looks almost like that, except it's a year or two newer. Mine is stereo, but has only a mono amplifier. Only stereo part is the volume control and balance. Even the tone controls are mono. :(


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 Post subject:
PostPosted: Feb Sat 05, 2011 5:11 pm 
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Joined: Nov Sun 08, 2009 9:48 pm
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Location: Fredericton, Canada
Thanks Tim: Thats good info. I have a few German radios with the flat pack bridge rectifier in them. I did install 4 In4007s in one but was afraid to try putting them inside the flat pack selenium case because I was afraid of shorting out in that confined space. Perhaps I'll give it a try in one of them. How did you insulate the diodes from the metal case? Did you just use black insulating tape?

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 Post subject:
PostPosted: Feb Sat 05, 2011 6:24 pm 
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Location: Santa Rosa, CA
Quote:
I install a Fairchild 1.5 amp 1000PIV round bridge, with a resistor inside.


Is there a resistor inside the bridge package?

Rich


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 Post subject:
PostPosted: Feb Sat 05, 2011 6:45 pm 
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Location: Baltimore, MD, USA
Believe it or not, our friendly Radio Shack still sells bridge rectifiers that would fit the bill. And they are usually conveniently located and reasonably priced. No, I don't work for them :wink: But I try to shop conveniently when possible.

http://www.radioshack.com/search/index. ... ifier&sr=1

The fourth one on the page is the one I use for my Scott amplifiers. Price is right...

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 Post subject:
PostPosted: Feb Sat 05, 2011 7:20 pm 
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Are the filter capacitors really 100-uF sections? If so, I would take Tin's advice and put a 27-Ohm or 33-Ohm, 5-watt wirewound resistor in series between the + terminal of the bridge and the rest of the set. The resistor should be outside any other packaging or housing from the old rectifier that you might "re-stuff" with new diodes.

With that much capacity, the inrush current would only be limited by the power transformer once the seleniums are replaced. The transformer is probably as old as the radio. No sense in abusing it now.

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 Post subject:
PostPosted: Feb Sat 05, 2011 9:24 pm 
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Location: Washington DC
I have used the radio shack bridge in many grundig, telefunken, etc. Cheap and reliable.

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