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 Post subject: Diode?
PostPosted: Dec Thu 07, 2017 4:34 pm 
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Joined: May Fri 11, 2012 5:07 am
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Hello
Been a while since I've been in here......
Not sure where to go with this problem so here it goes.....
I came into possession of a RCA Victor 1-BX-62 portable radio. There's a part I'm not sure about....It is sort of pink and has a type of ceramic coating that crumbles to the touch, as a matter of fact I could see the wire winding through the crumbled coating...... at first I thought it was a capacitor, then I thought it to be a wire wound resistor but I then received another radio that had a similar looking part in it ( crumbling ceramic type coating) that turned out to be a large resistor.
I looked at the schematic ( still learning how to read a schematic) but couldn't find the part. I tried to follow where the circuit lead to which is the power control. I looked at the schematic only to find a symbol that looks like a diode. The schematic doesn't give a value. The part has some printing on it ( as seen in the pics I attached) one side some what readable the other not so much.
The other radio with a similar looking part has numbers that correspond to the schematic parts list which did turn out to be a 3 watt resistor....It actually looks like a pink milk bone dog biscuit.
Hope this helps
Thank you in advance


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 Post subject: Re: Diode?
PostPosted: Dec Thu 07, 2017 4:45 pm 
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.5 would indicate a capacitor wouldn't it? Just because 2 components are next to each other in the unit doesn't mean
they will be on the schematic.

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 Post subject: Re: Diode?
PostPosted: Dec Thu 07, 2017 4:47 pm 
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Definitely NOT a diode or capacitor. Looks like a "fusible" resistor. Could be R10.

Rich


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 Post subject: Re: Diode?
PostPosted: Dec Thu 07, 2017 4:57 pm 
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Rich, W3HWJ wrote:
Definitely NOT a diode or capacitor. Looks like a "fusible" resistor. Could be R10.

Rich

+1 That is a fusible resistor.
That round yellow ceramic cap in the photo is probably C9.


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 Post subject: Re: Diode?
PostPosted: Dec Thu 07, 2017 5:33 pm 
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does the .5 refer to 1/2 watt ?
so it's basically fuse huh?

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 Post subject: Re: Diode?
PostPosted: Dec Thu 07, 2017 6:08 pm 
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glue_ru wrote:
does the .5 refer to 1/2 watt ?
so it's basically fuse huh?


Marking looks to read ".5 AMPS" The resistance is used to slow down the rate at which the fuse (the resistor) will blow which is needed when power is applied to absorb the initial surge.

https://www.vishay.com/docs/28909/acxxcs.pdf

Check the circuit downstream of it to be sure it didnt get hot or blow for good reason (assuming it is already)

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 Post subject: Re: Diode?
PostPosted: Dec Thu 07, 2017 6:25 pm 
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That is R-10 a 68 ohm sand resistor. Still looks Okay test with ohm meter if still within 10% it's still okay. The reason for being a sand resistor makes it flame resistant in case there is an overload. Do replace the stacked rectifier. No need for a dropping resistor it already has one C-10.


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 Post subject: Re: Diode?
PostPosted: Dec Thu 07, 2017 7:24 pm 
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I believe the photos show a selenium rectifier and a wirewound resistor.

The rectifier is M1 on the schematic, with the diode symbol. In the chassis photo, this is the part made with a stack of square red plates and an eyelet to hold it together.

The resistor appears to be R10 (68 ohms).

Both of these parts may still be full functional. The resistor can be checked with an ohmmeter. The rectifier might be checked by verifying correct B+ voltage when powered-up. Best to wait to do this until you have replaced the electrolytic filter capacitors. Bum capacitors can smoke the rectifier. Many will suggest replacing this rectifier with a silicon diode even if it is still functional, since they may not last too long in service.

If this is a portable radio with battery tubes, you should check the tube filament voltage and adjust the resistance at the R10 location to get the nominal voltage with your usual line voltage.

Ted


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 Post subject: Re: Diode?
PostPosted: Dec Fri 08, 2017 3:09 am 
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Thank you every one for the help.
I did an ohm meter check on what appears to be the resistor.....it checks infinity....the numbers just fluctuate all over the place! So it looks like I will be replacing it......seems like almost everyone agrees it's a 68ohm resistor.....maybe 1 watt? The stacked rectifier....is it what I read about as being a selenium rectifier?


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 Post subject: Re: Diode?
PostPosted: Dec Fri 08, 2017 3:24 am 
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I can see the marking that says "68". So the pink thing is the resistor and the red thing is the diode. There should be a 0.01 mfd (10000 mmfd) capacitor across the diode. As always, verify the actual identity of each component against the schematic and its connections.

Note: the parts list with the schematic shows this resistor as "fuse type." There's the possibility that another fault within the radio caused this resistor/fuse to fail.


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 Post subject: Re: Diode?
PostPosted: Dec Fri 08, 2017 9:27 pm 
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That picture tells all. The selenium diode AND the 68-ohm resistor need to go, both are rusted under the skin. Others will chime in as to values, ratings, etc. It's like you're expecting an original battery in an old car to work. Craig


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 Post subject: Re: Diode?
PostPosted: Dec Fri 08, 2017 11:19 pm 
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That resistor is for surge protection of the diode. 68-100 ohm should work. Based on the appearance of the original resistor and position, it's probably a 5W.

Most of us use 1N4007 diode for replacing old rectifier.

If you want to retain the fuse function, add a 1/2 amp fuse in series before the resistor.

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Last edited by AJJ on Dec Fri 08, 2017 11:38 pm, edited 1 time in total.

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 Post subject: Re: Diode?
PostPosted: Dec Fri 08, 2017 11:31 pm 
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Just install a fusible resistor, they are available from the major parts suppliers.
https://www.digikey.com/product-detail/ ... ND/2665481

Dave


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 Post subject: Re: Diode?
PostPosted: Dec Fri 08, 2017 11:40 pm 
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easyrider8 wrote:
Just install a fusible resistor, they are available from the major parts suppliers.
https://www.digikey.com/product-detail/ ... ND/2665481

Dave


Sounds like a good idea :)

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 Post subject: Re: Diode?
PostPosted: Dec Sat 09, 2017 1:24 am 
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They all sound good
Thanks again everyone!


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