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Old 8th Aug 2017, 7:04 pm   #61
bobskie
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Default Re: Loewe Radio Zwergsuper Opta 3516GW

I suppose that makes sense, that's a relief! It shouldn't be too difficult to convert it back to a valve looking at the diagram. I have replaced all the caps with broken ends(4) but I feel these German ones are probably quite reliable so I will wait and see how it works before replacing any others.
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Old 16th Aug 2017, 2:24 pm   #62
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Default Re: Loewe Radio Zwergsuper Opta 3516GW

Well I purchased a valve off eBay about a week ago and it's waiting for me at the post office so I thought I better crack on with this. I was going to rewire the valve holder but it's a bit of a daunting task. I located this component however which looks as if it has got very hot at some point. I am fairly sure it's the 30 ohm resistor connected into the 100 ohm resistor near the uy11 valve on the diagram, a picture is attached. Anyone have any idea why this could have happened? Running on 240V instead of 220V?
Interestingly the 100 ohm resistor is made up of 3 300 ohm resistors in parallel. I'm finding it hard working from the diagram I'm either missing things or the circuit has been majorly changed, I'm new to complex diagrams like this though so it's probably the former.
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Old 17th Aug 2017, 8:35 am   #63
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Default Re: Loewe Radio Zwergsuper Opta 3516GW

Quote:
Originally Posted by bobskie View Post
Anyone have any idea why this could have happened? Running on 240V instead of 220V?
It looks like something more serious than that. Maybe something went wrong somewhere else and shorted out, such as the smoothing capacitor. Make sure you check the other power supply components before applying power and use a lamp limiter when powering it up.


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Originally Posted by bobskie View Post
Interestingly the 100 ohm resistor is made up of 3 300 ohm resistors in parallel. I'm finding it hard working from the diagram I'm either missing things or the circuit has been majorly changed
The circuit has been changed when the metal rectifier was installed. It might also be that the circuit was originally the other version as posted in post 48. I wouldn't try to work out which bits that are there correspond to which bits in the circuit diagram as there will be differences anyway. I would just rebuild the power supply according to the circuit diagram. It's only a few components so shouldn't be too difficult. Don't bother with the 120V bits. Just rebuild the 220V section and upgrade the 520 Ohm resistor so that heater current is correct. With 100mA heater current it will be dropping 52V so at 240V supply it will need to drop 72V so 720 Ohms 8 Watts should do.
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Old 17th Aug 2017, 10:14 am   #64
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Default Re: Loewe Radio Zwergsuper Opta 3516GW

Yes I think i'll try and get it working with the rectifier first, maybe I won't even bother with the valve I think it could get a bit too confusing. A silicon chip could be the way to go and I'm sure I will be able to resell the valve here to someone who needs one. Of course it would be best to get it back to the valve but may well be beyond my capabilities. I still need to connect up the 16uf electrolytics but i'm struggling to work out exactly where they connect. I have also found another wire floating about completely loose that I have no idea where it came from!
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Old 27th Aug 2017, 2:31 pm   #65
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Default Re: Loewe Radio Zwergsuper Opta 3516GW

I ordered all the bits a need so far so just waiting on them arriving. I got 2 resistors to make up the dropper, the burned out resistor and the 16uf filter capacitors. Doing some poking around with a continuity tester I found the chassis was wired up to live(hence live chassis) but more worryingly it's got continuity through the screws on the knobs and the shafts. Is there any way to make this safer? Would wiring the neutral to the chassis work or even make a difference?

Cameron
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Old 27th Aug 2017, 2:46 pm   #66
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Default Re: Loewe Radio Zwergsuper Opta 3516GW

According to the schematic I'm looking at the neutral should not be wired directly to the chassis, mains neutral should be connected to the chassis via one pole of the on/off switch and the two bias resistors.

Lawrence.
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Old 27th Aug 2017, 4:46 pm   #67
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Default Re: Loewe Radio Zwergsuper Opta 3516GW

So should I swap the live and neutral over? Like I said I get continuity to the chassis through the live pin but not through the neutral.

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Old 27th Aug 2017, 4:55 pm   #68
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Default Re: Loewe Radio Zwergsuper Opta 3516GW

Look at the schematic in post#41, look at where the mains input conductors are, where the AC/DC sign is, the mains neutral conductor should be the bottom conductor shown in that schematic, the top conductor should be the mains live conductor.

Lawrence.

Last edited by ms660; 27th Aug 2017 at 5:08 pm.
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