Loewe Radio Zwergsuper Opta 3516GW

[bobskie]

Originally Posted by G6Tanuki

Without seeing a full circuit/schematic I can't tell you if this is a resistor or a thermistor.

Ah yes I should have attached a schematic, here it is. I have encountered thermistors before in a physics class but I wouldn't recognise one if I saw it.

[bobskie]

Originally Posted by ms660

The wave change switch on the schematic I'm looking at comprises of contact numbers 1 through to 22.

There are quite a few different diagrams, I think I have a print out of the one you are talking about I didn't realise those numbered parts were contacts. I think we are talking about the same thing and if so that should make it a lot easier.

Cameron

[ms660]

Yes we are looking at the same circuit, contacts 12,14,16 will be connected together same goes for contacts 18,20,22.

You can correlate that with the switch diagram on the schematic which I think is shown in the shortwave position, next position clockwise is medium wave, then long wave then gram.

EDIT: Looking around on Google there seems to be some different chassis layouts for this receiver so far as I can make out.

Lawrence.

[bobskie]

I think there is a more common chassis which I have and a rarer one with a different layout.

Cameron

[ms660]

Originally Posted by bobskie

I made a start on this today, replaced a couple of dodgy looking caps but I'm struggling to find the one in the space seen in the first picture on the circuit diagram, what does one of those back plugs look like on the diagram? The bulb circuit also seems to have deviated from the diagram though I could be mistaken. What is the component in picture two? A resistor?

Back plugs? Do you mean sockets on the rear of the chassis? If so, they are shown on the schematic as semi circular sockets as shown where the external antenna and earth connect to and also as the three pickup "tonabnehmer" sockets.

I'm not sure what the component in picture two is, whereabouts in the circuit was it?

Lawrence.

[bobskie]

It is disconnected on one side but looks as if it connects into the bulb. Thanks for the help,

Cameron

[Station X]

If the circuit is correct then it could be one of three resistors. Have you tried measuring it?

[bluepilot]

Pure speculation but as it's labelled 0.1A and the valves have 0.1A heaters it may be a thermistor for regulating the heater current. There appear to be circuit variations. Attached is another one with some variations in the power supply. Maybe that will give a clue.

[ms660]

Google Translate from the text in the first service manual link...

"In a part of the edition, the 5volt scale lamp is replaced by an 18volt 0.1amp lamp with simultaneous installation of a Urdox resistor 2410 Pl"

Lawrence.

[Station X]

It looks like the lamp is stamped 0.12A. I wonder what the voltage is?

[bluepilot]

"Urdox" is derived from "Uranium Dioxide". Later other materials were used but they all decayed in air so were generally sealed in a glass tube. This doesn't appear to be one of those. I wonder whether it's a different sort of thermistor that was installed originally or whether it was added at a later date.

[bobskie]

Originally Posted by ms660

Google Translate from the text in the first service manual link...

"In a part of the edition, the 5volt scale lamp is replaced by an 18volt 0.1amp lamp with simultaneous installation of a Urdox resistor 2410 Pl"

Lawrence.

It does indeed appear to be an 18v bulb, I thought this must be some sort of modification by a previous owner. I think I tried measuring resistance across it but I can't remember the result. I will check later.

Cameron

[bobskie]

I'm trying to measure it now but it's constantly changing which suggests it is a thermistor. It is in the 2 megaohms range now but has been up in the 3 and down in the one. I can't figure out if it's increasing resistance as it gets warmer or as it gets colder though.

EDIT - I put my crocodile clips on and let it settle and it's seems to be about the 2.2 mega ohm range at room temperature. Bringing a bulb in close seems to be bringing the resistance down, I was using my fingers to try to warm it before but I think I must have been changing the resistance.

[bobskie]

Another question is is the resistor pictured the dropper resistor? It's a 500 ohm 15W ceramic tube resistor. It is very far out and I will certainly need to get a new one but if it is the dropper what would be a better value for UK mains voltage?

Cameron

[ms660]

That could be the UY11 heater substitute resistor that would have been fitted when the UY11 was replaced with the metal rectifier.

Lawrence.

[bobskie]

Possibly I can't find it on the schematic, one end is connected up to the thermistor.

Cameron

[bobskie]

Further inspection today reveals more tampering had occured, on the voltage changeover section (marked spannungumschaltung on the schematic) a lot of wires appear to have been removed as shown in the picture, is this to only allow 220v operation? I have attached a picture to show what I mean. I can't really see the back row of connections very well but there are a few things attached on there.

[bluepilot]

Originally Posted by bobskie

a lot of wires appear to have been removed as shown in the picture, is this to only allow 220v operation?

Well, who knows whether the mods were made specifically to allow only 220V operation or whether the owner had 220V mains and couldn't be bothered reconnecting the 110V connections? I think that originally the rectifier valve went wrong and some mods were made to get the radio working with a metal rectifier. The owner did what was necessary to get it working and didn't bother with the 110V connections when he didn't have 110V mains anyway. (Just wondering whether you have actually checked that the radio is configured for only 220V or whether it could be only 110V)

I think you have to decide whether to restore it to its original condition or whether to leave it 220V only. Whatever you do you need to check it against the circuit diagram and make sure you have the correct components in the correct places. I think personally I would just make it 240V only then you avoid the possibility that it might accidentally get switched to 110V and damaged. You can increase the dropper resistors a bit to compensate for the increase from 220v to 240V.

[bobskie]

Yes I think that's what I'll do there is no point over complicating things. It has written on the back 220v only so I assume it has been converted for 220v operation. I have placed a bid on a rectifier valve so I can get rid of the metal rectifier and restore most of the wiring to original. I have still not found where that blue wire fell from though so there is still something else disconnected, it's going to take a long time to go through the whole diagram but I suppose I'll need to.


Cameron

[bluepilot]

Originally Posted by bobskie

I have still not found where that blue wire fell from though so there is still something else disconnected, it's going to take a long time to go through the whole diagram but I suppose I'll need to.

I wouldn't go through the whole circuit diagram trying to find out where it might have been attached. Just get the power supply working first by reconstructing what's in the circuit diagram. Then if the radio doesn't work try to find the faults. Maybe it will be obvious where the blue wire belongs when you find a fault. On the other hand it may belong to the power supply mods and not be useful for anything.