stern-sonn: 675/55GWU; Ilmenau

Good morning, radio friends

 

I am currently restoring a 675/55GWU radio and I downloaded the circuit diagram and the parts list from Radiomuseum.org.

When I compare the 2 documents, it seems to me that the parts list (ID 93036) does NOT correspond with the reality. I think that this parts list belongs to another radio. Is it possible to obtain the correct one, please?

 

Than the technical part: The 675/55GWU has also provision to receive FM (UKW), but I do not understand the circuit diagram.

Where is the FM detection?

What kind of detection has been used?

What kind of FM front end is this?

Is the IF (673 kHz) the same for AM and for FM?

What about the IF bandwith for FM reception?

 

Can someone explain this to me please?

 

mfg

 

Georges

 

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Parts list is now deleted.
Wolfgang E. look for a suitable list.

 

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Hello Mr. Campenhout.

Here a short description of the Functions for  this Radioset 1955/56.

 

Circuit Description from Hans M. Knoll Germany 02.2007

 

Stern Radio, Model „Sonneberg“

 

This AM/ FM- Radio is a cheap and simple  Circuit, I have never seen a lower quality.

 

The  RF Input has no Selectivity or amplification.

The Antenna goes through two IF- Traps (10,7Mhz) and a Balance- Transformer direct to the self –oscillate -additive -Mixer. His Output is formed from a 10,7 Mhz IF- Transformer (Bandfilter)    After the UCH81 follows a single -tuned -Circuit  (L20) with a coupling Coil L18.

After the UBF80 also follows a single -tuned  -Circuit (L22) with a coupling Coil L24.

 

The Demodulator is a single –Diode –Demodulator,  like in AM Radios used, called: “Flankengleichrichter” 

 

The first Units of lowprice Models on 1949/50 in W-Germany, use the same Technic in the IF-Part, not in the RF- Part.

Preselection with one Circuit was Standard.

Only Mixers with Multiplication (ECHxx) works some time like this, without preselection.

more here:korting_ukw_supereins_51w.html

 

The Demodulation do not works on Center of the Curve, she works on the left- or right- side of the Curve.  This Demodulator have no AM- Rejection.

 

The IF- Circuits are in Series upper side the AM lower side the FM Parts.

L 20 is shorted on AM -Reception.  The AM- Section is always in Function.

 

The Summ of  Band width  with the four IF- Circuits, must bee with, to prevent Distortion on the Modulation.  FM Deviation  +/ - 75 Kc must bee demodulated without  clipping.

regards Hans

 

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Here is a block circuit for "Ilmenau 675/55GWU"

Wolfgang Eckardt

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Herr Knoll,

Thank you very much for your useful information.

I find this radio  very interesting, although it is - technically spoken - of a minor quality.

It does not work for the moment, but I wonder what the reception characteristics will be in a country like Belgium, with a large quantity of FM transmitters on such a limited area

 

Once finished, I will report of the result.

 

Warm regards

 

Georges

 

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Hello Mr. Campenhout.

I will say: there was many of such quality Radios in the German Market

e. g. from my Company this one:

grundig_810_810w

This is a TRF  2 Kreiser on AM, the FM Part is equal but preselection in Front of Mixer _ Stage

If you have any questions later, whe will see what whe can do.

Also,  best regards Hans M. Knoll 

 

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Good evening, dear radio friends,

 

I am slowly progressing the repair/restauration of this set.

Unfortunately some components are totally missing (someone tried to repair the radio before), and I have not the knowledge to calculate the values of the missing components.

Missing are:

• A one watt resistor (R25, see circuit diagram please), in the return line from the output transformer to the second reservoir capacitor C53, which has been replaced (current value 47 µF)
• A smoothing capacitor C38, between resistors R18 and R20. According to the circuit diagram it is not an elko.

Who can help me here in choosing the value for these 2 elements?

A further remark: most of the paper capacitors are leaky, and I will have to replace them.

 

Best regards

 

Georges

 

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Hello Mr. Campenhout,

to start your restauration, place an 2 to 2,2 Kohm Resitor for  R20.

Later when the Radio operates,  and no one bring  a Partlist, i will help you to find the correct Value.
At moment only secure for Tubes is given and neccesary. The Voltage on C53 should have not more then 170 Volts, absolute limit: 200 Volts.. 

For C 38 you can use 0,22 to 0,47 uF. Greater Value ist recommendet. They reduce Hum on Audio.

With this values you can proceed.

regards Hans M. Knoll

 

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Guten Morgen, Herr Knoll,

In the meantime, I replaced all decoupling capacitors.

For R25 I used a 1200 Ohm 2 Watt resistor (I found this value in many other schematics of similar output stages)

For C38 I took a 0.22 µF one, as you suggested

After this the radio played, but with still a large amount of hum.

Then I replaced the elcos C45  (47 µF/450V) and C46 (100µF/40 V). C53 seems to be OK. The hum was better, but still there. Finally I changed the selenium rectifier by a modern Silicon one, and the radio works fine now!

Thank you again for your assistance

Warm radio regards from Belgium.

Georges

 

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