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 Post subject: Nordmende Arabella 57 (no audio)
PostPosted: Feb Fri 09, 2018 2:04 am 
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Joined: Feb Mon 13, 2017 10:46 pm
Posts: 158
Location: Atlanta GA
Hello,

Just got into this old German console today. Looks like it has never been worked on before. I powered it up with a dim bulb tester and all seems OK. I am getting 220 volts and 6.2 volts off the power transformer before it goes into the radio so I think that is good. Cleaned the switches with deoxit along with the volume pot. I have yet to check the tubes in a tester. All the tubes glow except the eabc80. I replaced it with a old eabc80 and now I have sound. Strangely the volume pot does not seem to make any difference on the volume coming out of the speaker. And when I turn the fm dial back and forth I am getting a lot of loud static and the strong stations in my area sound a little weak.

Any ideas what could be causing this loud static. It kind of sounds like the static you get on am when there is a thunderstorm in the area.

This radio has 5 different voltage settings, 110, 125, 150, 220 and 240. Should I set it to 110 or 125?

Also, the schematic shows 295 volts just after the selenium rectifier. However I am only getting 240v and all tubes are inserted. Should I be checking the voltage on the radio with the tubes removed or inserted?

Tomorrow I will replace the electrolytic caps and the paper caps. Does it sound like I should replace the selenium rectifier?

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 Post subject: Re: Nordmende Arabella 57 (no audio)
PostPosted: Feb Fri 09, 2018 2:03 pm 
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Location: Gretna, Nebraska
I would suggest using the 125 line voltage option for powering your radio.

Voltages should be measured with tubes in the radio.

You should definitely replace the electrolytic capacitors, and the wax paper caps before proceeding. Your set's voltage measurements can be affected by leaky capacitors which can load load down voltages in the radio.

Also be aware that other capacitor types like film and ceramic types are generally reliable and can be left alone unless
you have determined they have failed.

After replacing capacitors, you will be in a better position to evaluate the selenium rectifier, and other radio problems

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 Post subject: Re: Nordmende Arabella 57 (no audio)
PostPosted: Feb Fri 09, 2018 2:48 pm 
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Joined: Feb Mon 13, 2017 10:46 pm
Posts: 158
Location: Atlanta GA
Thanks for your response. Slowly but surely I am getting the hang of this.

What do you think of these white caps? They look like they are made of hard plastic to me. Do you think they should be replaced?

And, are those some kind of resistors on the speaker terminals? I have never seen this before. The last picture shows those speakers on the schematic as V7 and V8, they are the ones in the middle.

Thanks,
bb


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 Post subject: Re: Nordmende Arabella 57 (no audio)
PostPosted: Feb Fri 09, 2018 2:59 pm 
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Location: Montréal, CA
On the speaker are coils (cross-overs I think), not resistors. Those can go open only, so no need to touch them.

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 Post subject: Re: Nordmende Arabella 57 (no audio)
PostPosted: Feb Fri 09, 2018 3:51 pm 
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Location: Gretna, Nebraska
I would replace the white capacitors. At least one of them is a 4 uF electrolytic. Note the positive polarity band on that one. The rest are a range of values that are typically wax paper types and should be replaced.

While the outside case is plastic, the internal parts are likely a conventional wax paper design.
You could take one apart if you are curious how they are constructed.

Agree that that the devices on the speakers are AF coils for crossover. They are identified on the schematic as L56, L57, and L58 (I think).

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 Post subject: Re: Nordmende Arabella 57 (no audio)
PostPosted: Feb Fri 09, 2018 4:00 pm 
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Joined: Feb Mon 13, 2017 10:46 pm
Posts: 158
Location: Atlanta GA
Dumb question here but what is a "AF coil"? What does AF stand for?

Thanks,
BB


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 Post subject: Re: Nordmende Arabella 57 (no audio)
PostPosted: Feb Fri 09, 2018 6:42 pm 
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Location: Gretna, Nebraska
bluebellyyankee wrote:
Dumb question here but what is a "AF coil"? What does AF stand for?

Thanks,
BB


Audio Frequency coils, aka audio frequency chokes.

Coils are designed to be used at different AC frequencies. Some are used at radio frequencies. The coils used with speaker circuits are typically audio frequency coils, and are used to pass or block certain audio frequencies.

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 Post subject: Re: Nordmende Arabella 57 (no audio)
PostPosted: Feb Sat 10, 2018 4:48 am 
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Joined: Feb Mon 13, 2017 10:46 pm
Posts: 158
Location: Atlanta GA
Just finished replacing about 25 caps including the 3 filter caps. Those white plastic caps were paper inside and indeed they tested as bad as the normal paper caps. The radio slowly came to life as I progressed from one cap to the next. However I have a few issues.

First, I am not getting any sign of AM. FM works pretty good though but I am getting quite a bit of sound still coming through the speaker even though the volume is turned down all the way. Does it matter that I am using an old speaker on my bench instead of driving the 4 speakers that it should be if it was installed in it's cabinet?

Second, my B+ voltage is still 40 volts low just like it was before I replaced all the caps. I am getting 254v at the selenium rectifier instead of 295v that the schematic indicates and checking other voltage points down from there also come up about 40 volts low. So, is there anything else I should look at before I replace the selenium rectifier with a diode bridge?

Third, what do you make of this capacitor in the photos? It is a .01uf and a 10 meg ohm resistor all in one. One end lead has a green coating and goes to the volume pot, another end is striped red/green and goes to a terminal bar where another wire is attached and a bare wire goes to a socket that feeds the umbilical cord for the push-button tone control switches. The striped end and the bare wire is where it measures 10meg ohms. I replaced it with a normal .01 uf cap and I do not hear any problems but what should I do about this?

Thanks,
BB


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 Post subject: Re: Nordmende Arabella 57 (no audio)
PostPosted: Feb Sat 10, 2018 2:43 pm 
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Joined: Jul Tue 15, 2008 6:13 pm
Posts: 5105
Location: Gretna, Nebraska
Regarding the AM not working properly, have you cleaned any of the selector switches yet?

Most of these German sets with this style of selector switches are notorious for intermittent operation after years of accumulated dirt and/or corrosion. In most cases they will benefit from good cleaning with contact cleaner and repeated operation.

Same applies to tone and volume controls. While cleaning controls and with the set off, you may want to measure the resistance of the volume pot and verify it changes resistance value when adjusted.

The volume control may work better with the set's original speakers. Definitely worth trying it with them connected.

The lower than normal B+ could be from an aging selenium rectifier, although I would not change it out just yet. You may have something else loading down the B+ supply and I would rule that out first.
Be advised that if you do replace the selenium rectifier with a silicon bridge, your B+ voltages may actually be higher than the specified voltage. Silicon diodes have a lower voltage drop than a selenium rectifier does which can result in a higher B+ voltage.

I would just replace the combination cap/resistor with the equivalent separate components.

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 Post subject: Re: Nordmende Arabella 57 (no audio)
PostPosted: Feb Sat 10, 2018 5:19 pm 
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Joined: Feb Mon 13, 2017 10:46 pm
Posts: 158
Location: Atlanta GA
Yes I did spray the switches with deoxit and worked them over pretty good. I will do it one more time and see what happens. I also hope to get the tube tested today.

I am really concerned about this combination resistor/capacitor. If install seperate components would I simply connect a 10 meg resistor from that socket where the old bare lead was connected and then solder the other end directly to the lead of the capacitor? Since the old capacitor was maked with it's polarity and my new capacitor is not, should that be any concern that I attach the resistor to the correct side of the new capacitor?

BB


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 Post subject: Re: Nordmende Arabella 57 (no audio)
PostPosted: Feb Sat 10, 2018 11:16 pm 
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Joined: Jul Tue 15, 2008 6:13 pm
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Location: Gretna, Nebraska
Although that capacitor appears to be marked for polarity, it is in fact a non-polarized paper capacitor. Back then, paper caps were marked with a polarity to designate the lead connected to the outer wrap of the foil inside. This could be grounded to supposedly "shield" the capacitor from induced signals.
This practice now pretty much abandoned by most restorers, myself included.

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