Musikschrank 7063WF/3D

I'm restoring this model and could use your help.

I've replaced paper and electrolytic capacitors and tested all tubes but I'm still having two key problems.

1.  When tuning the AM broadcast band, signals whistle and oscillate.  Fine tuning sometimes clears it up, but adjusting the treble control which moves a ferrite rod into (an IF coil?) usually does the trick.  What might be wrong here?

2.  The FM band is distorted, even with an external antena connected, through most of the dial but is clear on one or two strong stations.  Is it just in need of a tuning? 

Thank you for any help you can provide.

Hi Tom,

Although I'm not as familiar with the details of these European radios as some of the other folks here, since no one has answered yet, I'll try to help you out.

The behavior you are describing on AM (whistles and oscillation) could be caused by oscillation in the IF stage.  I'm not familiar with the treble control configuration you are mentioning, nor can I see evidence of an adjustable core associated with the treble control on the schematic.  Nonetheless, such a configuration could be possible, since sharpening the IF bandwidth is actually a very intelligent way to trade off selectivity vs. treble response (bandwidth and fidelity).  If your radio really has such a device (to adjust a core in the IF with the treble control) it would make sense that moving the core would affect the tendency of the IF to oscillate.

There are a number of things which can cause the IF to oscillate, and this problem can be frustrating to track down.  Here are some things to look for:

1.  Poor ground connections in the RF or IF circuitry.  Look for connections to the chassis using rivets or screws.  Try cleaning, tightening, or hardwiring with soldered connections to connect the various ground points together.  Double check for any bad solder connections.

2.  Missing or bad bypass capacitors.  Check connections and values of capacitors which have one side grounded.

3.  Neutralization problems.  This radio has circuitry for neutralization of the IF stage.  See for example the two capacitors in series (10 nF and 8 nF) on the screen grid of the EF89.  Make sure those capacitors are both good and have proper value.

4.  Changes in component size, shape, or lead dress from the original.  If you've changed the wiring layout or location of components, try putting things back more in line with the way things were originally.

If all else fails, slightly detuning one of the cores in one of the AM IF transformers will lower the gain of the IF stage enough to stop the oscillation.  This will hurt the selectivity and sensitivity of the radio a little, but may be an acceptable compromise.

Your problem on FM could be one of the following:

1.  Bad ratio detector electrolytic capacitor.  This is the 10 uF capacitor shown just to the left of the EABC80 tube on the schematic.  Sometimes this capacitor is located inside the IF transformer housing, so you might have overlooked it when recapping.  If it's inside the can and difficult to get to, study the connections to see if you can add another 10 uF cap outside the can (ignoring the bad one inside).  Best case is if you can get to and replace the original cap.

2.  Alignment.  There are no alignment instructions for this radio here, so I would hesitate to monkey with this unless you're experienced with it.  After you've dealt with #1 above, if you still have distortion, one simple alignment step that sometimes helps, and won't get things too messed up is to adjust the secondary slug of the FM demodulator.  This should be one of the two cores on the second FM IF transformer (the transformer closest to the EABC80 tube).  I don't know whether this particular radio has the AM and FM IF transformers in a single can, or has separate cans.  If they're together, a little trial and error can identify which coils are for AM and which are for FM.  But there is risk of getting things misadjusted if you are unlucky.  If you think you can identify the secondary core of the FM demodulator, go ahead and adjust it to see if your distortion improves.  If adjusting it doesn't cure the problem, a more extensive alignment would be needed, and it would help to have alignment instructions from the manufacturer.

Best regards,

Tom 

EDIT:   to Mr. Thomas Albrecht:

Zitat:   Although I'm not as familiar with the details of these European radios as some of the other folks here, since no one has answered yet, I'll try to help you out.

My answer:

first post from TOM RAGAN was at 06,03.08 7:05

second post (above) from Mr. Albrecht  was at 07.03.08 7:19 its one Day for us !

sometime whe have other (own) jobs to do.

regards, Knoll

Adresse praezisiert am 21.03.08  knoll

Here's the moveable rod in question just below the banded resistor.  An interesting concept, this rod, which is connected by a cord attached to the treble control.  I've read other posts wherein the rod had a tendancy to stick if not used for awhile, easily resolved with scraping and some contact cleaner, in this radio it seemed to move with ease.

Thank you for all this great advice and I'll report back.

Back from a holiday I was confronted with this thread.

I would like to address two different topics:

1
Rule of 3 days waiting with an answer if a question can not be answered in a real professional manner.

I know that Thomas Albrecht is a very qualified person - and this as a human and as a professional in his job. Therefore this has nothing to do with him but with our principle which has probably not been addressed in English yet. Therefore I apologize that I come so late with this matter.

In the German speaking Forum we go so far that only about 75 editors can at all answer such questions posed to a model. The aim is to get real good answers because we also have the professionals who know how to deal with sophisticated radios which show some defects.

In the sections for other languages we have not introduced that only qualified editors may answer at all but I think we should introduce the rule that somebody answers only if he/she knows good answers - except there is no answer for 3 days. I hope that Thomas can enlarge and put into good English which is already linked to the forum main page as "Some examples of well done texts and help plus our forum rules." Perhaps some members write to him first what they would change or add?

I know that good cracks will not answer once guesswork has been started. Why should they?

2
Repairing/Restoring - "quick and dirty" or in a professional way?
This depends on the given set and/or on you and your goals. Everybody sees this question different therefore I can only split the readership by dealing with this question. It still has to be outspoken: The way depends first on your goals and your ability / sources.


a)
Quick and dirty: I know that often people just throw out the condensers and put in tubes which are reading "good" - and that's it. You can do so with simple sets if you only want to get them playing again and therefore this "quick and dirty" method is widespread. You even find it done here in Europe with more complicated radios from the 50ies - and therefore also many of those just working without their real quality reception ... That is the best case. the worst case is that you build in errors ...

Result: No learning process, a receiver which operates - often poor - sometimes not even that. Correcting this can be awful.

b)
The better way is to use one of the common techniques for error tracing which I have put together in the book "Radios von gestern" (in German). There are many good books on that in English and they are often found at auctions etc.

One of the techniques is to focus on the different stages like Power Supply, Power Amplifier, driver, second detection etc. The other is to use a Signal Tracer, doing more or less the same - especially if the set is not working at all. A third method is to listen to the problems and to work through the possibilities of causes until one has a good result. If possible then followed by an alignment.

If a set has been worked through without a solid method it can be hard to get it well again. A professional would rather help on an untouched set where the original development is still there. Many problems can arise by placing things differently or even changing grounding points.

c)
You can have professional help if you tell what you have done and what you can measure  (instruments and your ability). Such a helper has first to study the schematic (if possible) and do some other preparements if he wants to give a professional help for a sophisticated radio. Therefore don't expect an answer within 24 hours. In any case: Do use the link *** Please remind me *** or better "To activate e-mail notification for this board (or thread only)" to assure that you give an answer. Do tell if you will not be able to give an answer within short time.

Ernst,

Thanks for mentioning the 3-day rule, and also making a number of good points both for those seeking help and those wanting to provide help.  These guidelines are probably well known to the German-speaking community here, but perhaps not all of us English speakers had a clear understanding of this yet.

By mentioning that "I am not as familiar with the details of these European radios..." I hoped to leave the door open for one of the experts to followup with better information where appropriate.

Herr Knoll,

Sorry about not giving you enough time!  You are certainly one of the people I had in mind when I mentioned not being as familiar "as some of the other folks here" with the details of European radios (especially a Grundig!).

If you still are willing to provide some more expert advice than I was able to give, both Tom Ragan and I will very likely learn something useful for the future.  I often learn new things about German radios from your answers to technical questions.

Best regards to both of you,

Tom

Hello Grundig Friends.

Here is may Statement but only in German Language.

regards Hans M. Knoll