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Old 24th Nov 2023, 1:03 pm   #1
Pilot Mariner
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Default Grundig 3028 tone control unit.

Following on from this thread

Quote:
Originally Posted by Pilot Mariner View Post
Has anyone got a scrap 3028 chassis which has a good tone control thumbwheel unit, as the one I am working on has 2 broken levers which move the parts where the nicker elastic feeds through that gives a crude frequency curve.
I've had no luck in finding a scrap chassis, I therefore dismantled the unit to remove the levers and fabricate some new ones.

The originals seem to be made out of a thin paxolin type material. I can get my hands on sheet of paxolin or similar material but it is very difficult to cut into the desired shape without it cracking.

Has anyone any other ideas of making these levers or maybe using other thin sheet of something.

Mods pleas move if posted in the wrong section.

Thanks

Mark
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Old 24th Nov 2023, 5:39 pm   #2
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Default Re: Grundig 3028 tone control unit.

Depends what type of cutter you are using; but I reckon two possible options are:

1, Get them laser cut from plastic. Many companies offer this service, the cheapest in China but it does take 2-3 weeks for them to arrive.

2, Sandwich the Paxolin you can get in between two thin sheets of plywood (or MDF etc, or even thick card or plastic) this will reduce the likely breaks in the Paxolin. I have done this with some parts in the past for tuning dials etc. It works OK but you normally have to tweak the cuts a bit with needle files etc.

Have fun

Derek
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Old 24th Nov 2023, 8:34 pm   #3
MotorBikeLes
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Default Re: Grundig 3028 tone control unit.

Abrafiles. These are fairly malleable pieces of "wire" with abrasive teeth. They fit into a hacksaw frame. Three types from memory. Yellow coloured end is fairly fine, red is coarse. I think a coarser one, but not too sure.
They take a bit of getting used to. You break them (expensive) and as a result you learn not to break them, and you can get very accurate results. Not needed to buy any recently, but imagine Ebay could supply.
Yes, they can, use this to search "abrafile" blades
Les.
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Old 28th Nov 2023, 11:28 am   #4
Pilot Mariner
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Default Re: Grundig 3028 tone control unit.

Thanks for your suggestions.

In the end I fashioned the levers from an old sardine can which was strong enough and easy to cut with some good scissors. This did the job with some heatshrink on the middle part to prevent shorting out to the pot terminals (picture 1).

Whilst I had the unit in bits, I sandblasted the rather grubby corroded bracket (picture 2) clean (picture 3).
It looks like this set had suffered a spillage at some point or someone adjusting the controls with wet fingers.

The final picture shows the completed re-assembled unit with the levers connected.
Hope this helps if someone else comes across this problem.

Mark
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Old 28th Nov 2023, 12:33 pm   #5
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Default Re: Grundig 3028 tone control unit.

I hope the holes are clean and don't cut through the plastic pin. Perhaps a little grease might help.
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Old 28th Nov 2023, 12:57 pm   #6
stevehertz
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Default Re: Grundig 3028 tone control unit.

Excellent job Mark! Something a bit fishy about it though.
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Old 28th Nov 2023, 1:46 pm   #7
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Default Re: Grundig 3028 tone control unit.

Well done Mark.
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Old 28th Nov 2023, 1:47 pm   #8
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Default Re: Grundig 3028 tone control unit.

Yes well done. Simplifying the pivot holes to eliminate the snap on action obviously made things easier. Did you have any problems attaching the levers to the existing pivots?
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Old 28th Nov 2023, 2:25 pm   #9
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Default Re: Grundig 3028 tone control unit.

Quote:
Originally Posted by vidjoman View Post
I hope the holes are clean and don't cut through the plastic pin. Perhaps a little grease might help.
Yes good point. I used the Polish Graal Filety z makreli w oleju (makerel fillets in oil) as I find the metal slightly thicker than the standard sardine can.

I also oversized the holes and hopefully used a good drill bit. The original levers broke because the indicators were seized. They are now fairly free and the thumbwheels don't need much force to operate them, so I hope it will last a few years, but I will put a dab of grease on the pins just in case.

Mark
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Old 28th Nov 2023, 2:34 pm   #10
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Default Re: Grundig 3028 tone control unit.

Quote:
Originally Posted by Station X View Post
Yes well done. Simplifying the pivot holes to eliminate the snap on action obviously made things easier. Did you have any problems attaching the levers to the existing pivots?
It was a bit fiddly getting the inner ones on Graham because at the thumbwheel end there is a piece of plastic which rides up against the pivots which looks like it is designed to stop the levers coming off.

On the indicator end (not sure what they are called), I just dabbed the soldering iron on the end of the plastic pivot to stop the levers coming off.

Mark
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