Telefunken Operette 6

Thread Starter

8302

Joined Nov 24, 2022
17
Hello, I am hoping to get a little information and advice concerning a project I have started. It is a Telefunken Operette 6 radio that was recently given to me. I am not an electrical engineer or technician, just a new hobbiest.
When I got the radio I plugged it in to see if it worked (I now know, wrong thing to do), it would receive fm signals but there was a loud humming in the background. Some research I’ve done tells me this is probably due to a faulty filter capacitor. I plan to replace all of the paper caps in the radio but am unsure about where the filter cap is located. The schematic is written in German which makes it very difficult for me to understand. I found a key for German electrical symbols on line but it is also written in German! I have included 2 attachments, one is the schematic and the other is a picture of what may be the filter cap or maybe a rectifier.
I read with interest a posting from a few years ago pertaining to the same radio but they did not identify the black AEG component, at least not to my understanding. Any help in locating the filter cap will be greatly appreciated. 1C363514-F7EB-481A-AE2B-4B6B429E0AA5.jpegPNG image.png
 

bertus

Joined Apr 5, 2008
22,120
Hello,

The black device is the rectifier. (it states gleichrichter on it, wich is german for rectifier).
It can handle 250 Volts at 75 mA.

Bertus
 

LesJones

Joined Jan 8, 2017
3,899
The 50 uF capacitor tht Dave points out seems to be smoothing for the anode supply of the output stage but the other 50 uF capacitor smooths the HT to the rest of the unit and the screen grid of the output valve. This comes via part of the winding on the output transformer which seems to be used like a smoothing choke.

Les.
 

MisterBill2

Joined Jan 23, 2018
13,741
The second filter capacitor is above the first cap in the circuit sown in post #6. If the hum persists it may possibly be a rectifier problem as well.
 

MisterBill2

Joined Jan 23, 2018
13,741
What looks like just using part of the audio output transformer is a means to reduce the tendency toward magnetic saturation of the transformer by the output tube's plate current. It works fairly well, allowing less distortion without adding more iron to the core. But it does look strange when looking at the circuit.
 

LesJones

Joined Jan 8, 2017
3,899
I suspect the large black cylindrical thing in your first picture could be one of them. (They will almost certainly be electrolytic capacitors.) It is also possible that the two capacitors are in the same can. If this is the case you will probably find it difficult to find a drop in replacement. You will probably not be able to find 50 uF capacitors in modern components. The nearest will be 47 uF. these will be OK. Make sure that the voltage rating is the same or higher than the originals.

Les.
 

MisterBill2

Joined Jan 23, 2018
13,741
That tall black cylinder in the photo in post #1 looks like it would be the filter capacitors. My guess is that it has three terminals o the bottom below the chassis. On the drawing,I think that I see voltages posted near those capacitors on the circuit.
If that device is the filter/smoothing dual capacitor, the replacements will probably fit easily below the chassis, but you will need to add some terminals for the connections.
A photo of the bottom view may also show us the rectifier, which might possibly need replacement if it is a selenium type device.
Those have been known to develop reverse leakage faults.
 

Thread Starter

8302

Joined Nov 24, 2022
17
Bertus pointed out that the black thing said “gleichrichter” on it and that is German for rectifier. I will add a photo of the bottom in a little bit. It may show where the filter caps are located. Thank you all for your help!
 

Dodgydave

Joined Jun 22, 2012
10,591
Bertus pointed out that the black thing said “gleichrichter” on it and that is German for rectifier. I will add a photo of the bottom in a little bit. It may show where the filter caps are located. Thank you all for your help!

It would seem that it has a selenium rectifier in Black, I would replace it with a silicon type 8A 500 V ( picture) and the smoothing caps are in aluminium cases. (14 mins into the video..)

tumbnail_3d0f47f0-e3d6-4aac-b40e-597362116557_3.jpg

 
Last edited:

MisterBill2

Joined Jan 23, 2018
13,741
OK, so it is the rectifier, selenium, as I had guessed, not the filter cap. More terminals to add to support the new smaller components. But the radio will perform better than before.
 

Thread Starter

8302

Joined Nov 24, 2022
17
Thank you for the link, I had seen it before but forgot that he pointed out the rectifier and filter can. I am thinking of disconnecting the filter can on the bottom of the chassis and adding two 50uF filters there, or 47 uF if I can’t find the 50s. I am including a pic of the can from the top and bottom. I also have a pic of the bottom of the rectifier, I sincerely hope that that I don’t have to replace it because it is well hidden!CF0A9C21-A7D7-430A-ADBF-5965A13150C4.jpeg287147E6-56FC-4A54-931D-96C1CA39DB28.jpeg3BB4C102-357D-4D33-89EE-4270EF09FC70.jpeg
 

MisterBill2

Joined Jan 23, 2018
13,741
Theone photo shows what I am guessing is the bottom of the dual 50 mfd capacitor connection, with the three tabs soldered to the chassis.
What I do not see is the bottom of that black cylinder that is apparently the rectifier. If is is present it is indeed very well hidden.
 
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