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 Post subject: Olympic Opta 5711W / Selenium Rectifier > Diodes
PostPosted: Sep Fri 07, 2018 9:18 pm 
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I'm working on an Olympic Opta 5711W with a selenium rectifier that I want to change to diodes (IN4007). In the past I've installed a single diode and a resistor to to replace a selenium rectifier but not multiples.

If someone could help me with instructions as to how to connect the diodes inside the selenium case it would be greatly appreciated.

Thanks,
Richard


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 Post subject: Re: Olympic Opta 5711W / Selenium Rectifier > Diodes
PostPosted: Sep Fri 07, 2018 9:48 pm 
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Location: Mountains of Mourne. Ireland.
You need to replace it with a silicon rectifier...
Scroll 2/3 down this page and see...

Selenium (semiconductor) Rectifier
German radios typically used...
http://www.mbzponton.org/n2awa/grundig2066px.html

If you are unsure how to connect it Richard, ask and someone will draw you a sketch.

Greg.


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 Post subject: Re: Olympic Opta 5711W / Selenium Rectifier > Diodes
PostPosted: Sep Fri 07, 2018 10:19 pm 
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You connect four 1N4007 diodes per the schematic or buy a modern bridge rectifier (like the one mentioned in the article).


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 Post subject: Re: Olympic Opta 5711W / Selenium Rectifier > Diodes
PostPosted: Sep Fri 07, 2018 10:29 pm 
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Thanks for the information and the link.

I ordered the parts from Mouser so will get back in touch asking for help with the wiring when I get the parts. After reading the information in the link it sounds as if adding a 50uf cap after the dropping 10w 100ohm resister will be necessary.

Richard

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 Post subject: Re: Olympic Opta 5711W / Selenium Rectifier > Diodes
PostPosted: Sep Sat 08, 2018 3:51 am 
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Every radio is a bit different, so the necessity of adding anything can be determine later.

I'd suggest finish all your restoration work along with the new bridge rectifier first. Then let measured voltage guide your next move. If B+ is not in acceptable range when compared with the schematic, then add the approriate resistor and whatever else.

When I restored my Grundig 4070; after installing the new bridge rectifier, the voltages measured spot on, so additional mods were unnecessary. Not every case is the same.


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 Post subject: Re: Olympic Opta 5711W / Selenium Rectifier > Diodes
PostPosted: Sep Sat 08, 2018 7:48 am 
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Joined: Jan Tue 31, 2012 1:55 am
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Location: Mountains of Mourne. Ireland.
For Power Resistors (that get hot to touch and require heat dissipation) you can also use an Aluminum chassis mount type as seen here along with a couple of ceramic/cement types, (all wire wound).
Image

Here are some (below) as deployed by Gary aka Radio Fixer when replacing a Candohm (multi-section) resistor.

Image
image: Gary aka Radio Fixer. viewtopic.php?p=2742147#p2742147


Greg.


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 Post subject: Re: Olympic Opta 5711W / Selenium Rectifier > Diodes
PostPosted: Sep Sat 08, 2018 6:01 pm 
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I ordered the silicon bridge from Mouser but had the IN4007 diodes and the 10w, 100ohm resistor on hand. With time on my hands I decided to try my hand at installing 4X of the diodes in the SSF case. I was pleasantly surprised that I pulled it off. The voltage is spot on at 250v.

The radio plays but I do have an issue with excessive base. The only tone selector where the sound is acceptable is voice. The others–base, jazz, and orchestra are booming, especially on strong stations. The radio has been recapped with the exception of a single 2uf electrolytic which I ordered from Mouser. I have my doubts that the 2uf electrolytic is the cause of the base issue since the radio was playing better before the switch to the diodes. I can post the schematic if that would be helpful. There were a couple of wiring issues with connections to the old selenium rectifier that I repaired. In fact the white wire may not have been connected to one of the ~ tabs. The yellow wire was a good connection to the other ~ tab.

At this point I'm not sure about where to start looking for the problem with the tone selectors. From the beginning the sound was not as good as you would expect so I'm thinking that fixing one problem is magnifying an issue somewhere else.

RB

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 Post subject: Re: Olympic Opta 5711W / Selenium Rectifier > Diodes
PostPosted: Sep Sat 08, 2018 8:42 pm 
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I think you're right about not trying to "fix" something that you're not sure about. Maybe there's supposed to be lots of bass with "voice" not selected.

3 things to check:

- If the sound problem is only on FM and maybe if there's some distortion, wait until you've replaced that (C2) 2mfd electrolytic capacitor. It's part of the ratio detector circuit. Note that the orientation on the schematic is correct (not wrong).

- Also take a look at that 50mfd (C3) capacitor on pin 3 of EL84. A higher capacitance is supposed to result in better bass response, but not excessive bass. Just take a quick look to see if everything is connected correctly there.

- Tone control circuit on this radio has only two components. C54 (0.025 mfd) passes high frequency notes through potentiometer R1 (500k). When R1 is adjusted low (low resistance), more high notes are bypassed resulting in more bass. If you disconnect C54 (disable tone control competely), there should be more high notes/less bass. So check that circuit. Was C54 replaced?

Note that the "voice" selector's job is only to bypass that 200pf (C55) capacitor. You can check that plus C59 and R32 too if everything else seem ok.


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