Grundig spare parts and Telefunken Decoder problem

Dear members, I'm new of your group.
I live in Venice - Italy.
I love the restoring (and the listining of course) old German radio.
I prefer the 1952 to 1967 production.
I repair radio for my friend also.
Often I need spare parts for those radio. Usually I bought it on ebay, but sometime it's very difficult to find it.
Do you know an online shop?

Now for example I need a tast (or only the metal tast-cover) for a Grundig Stereomeister 300 or 3000.
Anyone know where I can buy it?

Another little problem.
Telefunken Opus 2550.
When I listen FM in Mono mode the sound is good, but when I push the Stereo switch I listen a distorsion at low frequency.Under like 300 Hz the sound is very noised.
Anyone had solved the same problem in past?

Kindest regards
Giovanni Saoner

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Dear Giovanni,

"a good antenna is the best amplifier" ! This problem is very often underestimated. In case of stereo you need much more RF-input voltgage than for mono. Therefore (in general) built-in dipoles will not lead to an optimum of radio reception. Did you take this into account ? What kind of antenna do you use?

Best regards
Rolf

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Dear Rolf,
sorry the delay but I was outside Venice until today.
Thank you for your suggestion, it confirm my experience, but the antenna is the inside building and it work fine.
I have anoter similar 2430 and it sound perfectely with it's own antenna.
I think is the decoder that don't work correctely, but I don't know exactely how can I measure (with oscilloscope) in the decoder test point.
Maybe I can try to change all the capacitors and diodes in the decoder ciruit, but I don't like to work in this manner.

Do you know anyone for sell to me spare parts, and particulary a Grundig Stereomeister 300 tast ?

Thank you for reply to me.

I'm planning to contribute to this fantastic comunity with my diagrams, images and books.
I'm installing the scanner to my house.
Kindest regards
Giovanni

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Dear Giovanni,

1. please do not change any capacitor or resistor with the exception of electrolytic types which are in general used only for power supply an similar purposes. And do not turn any coil core !

2. However, if mono reception sounds okay this does not automatically mean that also stereo will work. There are many possibilities of a fault before the decoder input, e. g. of IF-alignment or ratiodetector.

3. I got into difficulties to help further on because I did not find the wiring diagram of the opus 2550 in RM.org. Seems that the decoder is working with an ECF 80 tube (?). Have a look into the wiring diagram, if possible. You have to measure all voltages, I hope that some are stated there. If the voltages are within the limits, please tell us here. And do not forget about uploading the wiring diagram if it is available for you.

Best regards
Rolf

P. S. In case of the Stereomeister spare parts I am sorry, but I am not able to help you.

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Hello,
I added some schemes: Graetz Stereo Unit 250 25H, and Telefunken Opus HI-FI 2430.
I have also the Service Manual for the 2550 but I found all diagrams on our website.
Why you cannot see it?
There are 3 pages on Telefunken Opus 2550, only one is correct.
I will write to propose to erase of the incorrect pages.

Can you kindly watch the 2550 decoder diagram and try to help me?

Giovanni

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Dear Giovanni,

sorry, but at this locations No 1  , No 2  and No 3 for opus 2550 I found no wiring diagram at all.

Today I was looking at No 4, but it is for opus 2430 !

For 2430 equipment are several diagrams existing including a stereo decoder. Maybe that the 2550 has the same decoder. So I tried to cut it out, enlarged it and marked several voltages which you would have to check, see below.



Good luck and best regards
Rolf

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Hello all

I'm thinking about buying a Telefunken Opus 2550 / 2430 to my collection. When seeking info about this radio, I have found this thread. I like so much to learn how the now old radio engineers made a lot with a few components. So examinating a stereo decoder made with only one vacuum valve is a very rewarding exercise to me ;-). 

But after a few checks while figuring how this decoder runs, I'm shure that this schema is not correct.There is a wrong connection on the output transformer. I've made a correction (red X ).

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Well, it's one bottle, but two devices.

This is even more minimal. A single pentode Grundig Stereo Decoder.

I hope to make a battery valve (tube) radio based on this :)

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Hi Michael

Amazing !!!. I have read those thread about this grundig reflex decoder, and it's impresive. And learned too about a modern mos-fet as direct replacement of some old valves. I know that a Mosfet is very similar to a Triode /pentode, but as much as a direct replacement....

All those reflex circuits take me back to my early days in radio, when 12-14 years old, to an AC126 germanium transistor cost me several weeks' pay. How long..

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