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Old 4th Aug 2022, 9:29 am   #1
jascha
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Default Grundig TK9 (TK12) Unidirectional pulley springs failure. Expert help needed please

Hi everyone,

I have rescued a beautiful Grundig TK9 which I got it all working after spending hours recapping it, fitting a new pinch roller from another machine (had to make a new bushing to fit it) and so on and after almost finishing the job happily to start using it, the UD drive pulley springs suddenly failed on me. They unravelled and tried to refit them but to no avail as they got deformed. I spent hours yesterday trying and trying to rescue them but sadly I am out of luck.

This model makes use of bi directional playback and recording hence the mechanics of it all with these clutches and pulleys. It looks to me that i need to have 4 springs made to rescue this machine, 2 wound in clockwise and the other 2 anticlockwise. I do have a lathe and can have the patience to wind these springs even though i never did such a task however I need some help please, unless someone has been in this situation already and has made these springs to rescue a similar situation.

I measured the springs' diameter and thickness of the material however I do not know the exact length of how long they should be. I guess they have to be roughly 18cm and 30 cm long (2 of each). I attach photos and some description which I took from the Hellyer's book.

Any assistance is hugely appreciated to get this beauty back and running, especially as so much time was spent to restore it.

Thanks
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Old 4th Aug 2022, 9:30 am   #2
jascha
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Default Re: Grundig TK9 (TK12) Unidirectional pulley springs failure. Expert help needed plea

Here are some more photos.
Thanks
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Old 4th Aug 2022, 6:49 pm   #3
ricard
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Default Re: Grundig TK9 (TK12) Unidirectional pulley springs failure. Expert help needed plea

I remember going to the local Grundig service center and buying a set of these over the counter. This was back in 1978, but I remember being impressed that they had spare parts for a then 20-year-old machine. The sales person was quite young yet still seemed to know everything about the machine. A long time ago now ...

Anyway, can't really offer much concrete help, except that I think the same clutches are used by the larger machines such as TK819 and TK830 and possibly others as well (easily recognized by the same 3 + 1 + 1 button arrangement) which may extend the range of potential doner machines should that be the only viable optoin.
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Old 4th Aug 2022, 8:25 pm   #4
jascha
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Default Re: Grundig TK9 (TK12) Unidirectional pulley springs failure. Expert help needed plea

Thanks for your reply Richard. Yes the only solution it seems is to find a donor machine to take parts from and substitute. Shane though having to destroy one machine to save another.
I have spoken to a friend of mine who repairs clocks and he will rise to the challenge and try to manufacture a set of 4 springs for me and see if he can get it to work. One should never give up and from what you Des rive it sounds like they can just be fitted relatively easily. Mine got stretched and mangled and the only solution is to replace them rather than save them. I tried for hours but itís impossible to refit springs when they have been abused by the machine itself.

Cheers
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Old 4th Aug 2022, 10:28 pm   #5
Roy
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Default Re: Grundig TK9 (TK12) Unidirectional pulley springs failure. Expert help needed plea

I had a similar situation with a TK12. For some reason the clutch was out of adjustment and the gap had opened up sufficiently for the spring to escape. It seemed like a disaster at the time, but I was able to recover it by cutting out the mangled section and refitting the remaining undamaged length, which was of course very much shorter than it should have been. I cannot recall the exact details because it was a long time ago, but although the spring had very few turns left, it worked fine. The gap needs to be adjusted very carefully (almost completely closed) so the spring cannot possibly escape again.

Do you think you have enough undamaged spring left to give that a try?

Best of luck with it.

Roy
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Old 5th Aug 2022, 12:19 am   #6
dmaillard
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Default Re: Grundig TK9 (TK12) Unidirectional pulley springs failure. Expert help needed plea

Hi,
You do not need the full length of the spring for it to work, as Roy stated. Cleanly cut off the damaged bit, carefully clean the cut area of any burrs & reinstate the remaining spring. Its a common issue with these decks.
The other issue you're going top face with these decks is the hardened foam rollers causing uneven contact with the heads resulting in poor playback. You need to replace the foam with something suitable, the foam needs to be soft with an even surface.

Last edited by dmaillard; 5th Aug 2022 at 12:24 am.
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Old 5th Aug 2022, 9:47 am   #7
ricard
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Default Re: Grundig TK9 (TK12) Unidirectional pulley springs failure. Expert help needed plea

So the reason this happens is simply that the gap for whatever reason opens enough for the spring to be pressed out? Would this simply be the result of the grub screws holding the outer parts of the clutch in place loosening?

I'm impressed by the mechanical design of these machines. With the clutches, and one solenoid for the pinch roller and two more under the reel tables, one gets a completely relay operated machine with a single motor.

The larger TK819 etc machines have two electrically selected speeds and a direct drive synchronous motor. Also quite impressive for this class of machine. I suspect though that they were rather expensive in their day.
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Old 5th Aug 2022, 10:44 am   #8
DMcMahon
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Default Re: Grundig TK9 (TK12) Unidirectional pulley springs failure. Expert help needed plea

I have a TK 9 which I have not yet looked at and also a TK 819.

Do not remember seeing these springs on the TK 819.

Are the springs easy to get to/remove for measurement purposes or are they best left undisturbed ?

David
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Old 5th Aug 2022, 3:10 pm   #9
jascha
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Default Re: Grundig TK9 (TK12) Unidirectional pulley springs failure. Expert help needed plea

Thanks so much for your responses. I have been inspired by ideas and am trying another option of straightening in a vice the bad portion of the spring, then under tension rewind the bad part of the spring by hand whilst clamping the axle in the lathe. I think if I manage to straighten part of the spring I might be in luck. If this fails then I will try cutting the bad part but am afraid it might not be enough spring left to respectively connect the two adjacent parts together.
I attack a photo of my attempt so far.

Cheers
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Old 5th Aug 2022, 5:20 pm   #10
jascha
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Default Re: Grundig TK9 (TK12) Unidirectional pulley springs failure. Expert help needed plea

I think Iím winning . Itís a tedious job but thanks to the advice especially to the idea of not letting the spring escape. I tried not to cut any sections and it seems to have worked. I still have the other to do but at least itís not all lost. Phew!
Thanks again guys
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Old 12th Aug 2022, 3:28 pm   #11
DMcMahon
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Default Re: Grundig TK9 (TK12) Unidirectional pulley springs failure. Expert help needed plea

Sounds like you are doing very well. So it looks like the springs would not normally be visible unless the pulleys are stripped down, it explains why I do not remember seeing them before.

David
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