grundig: 5060a ; Flexible Cable Repair

Grundig models 4090, 4095, 5060, and 5060a have variable AM bandwidth.  The bandwidth is varied by rotating the highest frequency tone control.  This control rotation moves a tuning slug in the first AM IF transformer through a flexible cable.  According to the Grundig alignment instructions (available on the 5060a model page), the bandwidth in these models varies from 2.5 to 7.0 KHz as compared to similar fixed-bandwidth models 3060, 3068, and 4085 that have bandwidth of 4.3 KHz.

The flexible cable has a steel jacket and plastic core.  This plastic core shrinks substantially both in length and diameter.  The shrinkage in length causes a restriction in the range of motion of the highest-frequency tone control, eventually to where the control may not rotate at all.  The shrinkage in diameter causes "lost motion" so that the tone control can be moved over a portion of its range without moving the IF transformer slug.

These problems are eliminated by replacing the plastic core of the flexible cable with an insulating material of the correct diameter.  After some experimenting I used .039" (1.0 mm) Teflon spaghetti (bus wire tubing).  It would be best to insert a short piece of bus wire inside the spaghetti at each end where it is clamped to reduce crushing of the spaghetti.  A nice feature of using Teflon is that it is self lubricating, allowing for smooth operation.  Ross Hochstrasser, of the Bavarian Radio Works (Massachusetts, USA) stated that he uses filament for a yard string trimmer (weed whacker) for this repair.  So there is another idea for core material.

Coarse adjustment of the cable is made by adjusting the position of the IF slug clamp on the cable core.  Fine adjustment is made by screwing the end fitting on the IF transformer end of the steel jacket in and out of the mounting bracket.  This fitting turns since it is not attached to the jacket, but the locknut must first be loosened.  (This fitting should be set in the center of its adjustment range while making the coarse adjustment of clamping the IF slug to the flexible cable core.  This adjustment is not critical at all for the operation of the radio as long as the tone control can travel over its full range.  As long as the cable core is properly sized so there is no lost motion, the length of IF transformer slug travel is only slightly longer than the cable core travel, and this excess travel should be centered so that the slug is not at the end of its travel at ether end of rotation of the tone control.

I have been informed by a gentleman who previously worked for Grundig that AM IF alignment should be done with the bandwidth control set at the "narrow" end (least amount of treble sound).  This detail is not addressed in the alignment instructions.

I have attached a photo of the flexible cable installed in my 5060a after the repair was complete, and also photos of the clamps that attach the cable core to the tone control and the IF transformer slug.

Paul Moyer

Attachments:

• Complete flexible cable (65 KB)
• Flex Cable - Tone Control End (47 KB)
• Flex Cable - IF Transformer End (44 KB)

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Hello Paul,

 Thank you for posting good hints about the repairs to the ZF (IF) bandwidth control cable.
 I have been using piano wire with good results and no apparent ill effects on the circuit.
 Ross' idea of using common nylon string trimmer line seems an elegant solution. I will try this on the next repair of this type.
 
 The note about setting the ZF for narrowest bandwidth prior to stage alignment is good.
 Not all Grundig alignment notes state this precaution, though I have seen it stated on some documents.

 The reason for my query in another post for this model 5060A regarding any published specifications or mechanical dimensions for adjusting the control cable travel- stop-to-stop, stem from having read of published specifications for this adjustment elsewhere, for different brands/ models.

 (i.e. Tone control full clockwise, cable clamp so many mm. from IF base bottom, etc.)

 Considerable variation of coil form travel and tone control potentiometer can be so adjusted within the ranges of full travel of each item. Meaning, the stops for each component do not automatically coincide.
 I was wondering if Grundig had information of this sort published as well, other than just the frequency range so stated in the alignment documents.
 If no simpler answer, then I suppose I will resort to AM sweep and oscilloscope to find out .
 
 Regards,
 Dennis Daly

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Paul,

This is one fantastic piece of restoration!

I hope that this thread is linked to other sites, because this solution could work for other radios too, in fact, the Grundig Satellit has cables that are sililar to this one.

Thanks for the pics too.

Check out the Irfanview thread, it is amazingly useful for pics and schematics to this site and to others.

I would like to thank Mr Birkner for his time and explanation in using this program!

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Paul, did you ever find any alignemnt instructions?  

Also, I need a glass dial scale for mine.  Would any of you happen to have one?  Bear in mind that the U.S. version is different from the European version.  I need the U.S. version.  Picture attached for reference to what I'm looking for.  Thank you for all of your help! :)  

 

Attachments:

• picture of glass dial scale for U.S. Grundig 5060A (284 KB)

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