I am trying to refurbish a 1970s quality Grundig portable (it's either that or have a nap on Good Friday afternoon !) and the sliding volume control is crackly and sometimes cuts out.
If I remember my youth accurately I recall rubbing a soft pencil (carbon) along the round potentiometer (?) of dodgy radios to improve the crackles. Is there anything else I can do? Is there a spray ?
I'm not going to bother trying to source a new volume control.
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WD40 and a cotton bud to clean it. Its probably full of old soft pencil. If you can slide a thin strip of emery paper under the metal slider contact to clean it that will help.
Ideally this stuff
www.taw.eu.com/index.php?main_page=product_info&products_id=52
Is better.
Last edited by: Zero on Fri 22 Apr 11 at 14:02
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You would probably know better than me Zero but isn't there a possible issue with WD40 disolving the tracks on some pots... if they had a carbon surface or something like that. I know I was advised never to spray it into the pots on my 70s PA amps.
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WD40 shouldn't disolve anything.
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It dissolves tar splatter on the side of my car.
Last edited by: Fullchat on Sat 23 Apr 11 at 21:40
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>> It dissolves tar splatter on the side of my car.
If he has got tar based variable resistors no wonder it crackles!
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Iso-propyl alcohol is usually recommended for cleaning purposes, certainly not WD40 as although it's not a good oil, it is still oil in a major part, and thus electrically insulating.
I got a bottle of iso-propyl alchohol from a chemist, not too hard to get.
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The crackle is caused by inconsitent conductivity between the carbon track and the wiper. The dirt in fact lifts the wiper off the carbon track
WD 40 provides a consistent conductivity between the two, and the film left behind is not thick enough to act as an insulator.
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WD 40 is a 50 per cent solvent - mineral spirits - so it will dissolve grease.
www.wd40.com/about-us/myths-legends-fun-facts/
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50%: Stoddard solvent (i.e., mineral spirits – primarily hexane, somewhat similar to kerosene)
Evaporates
25%: Liquefied petroleum gas (presumably as a propellant; carbon dioxide is now used instead to reduce WD-40's considerable flammability)
Evaporates
15+%: Mineral oil (light lubricating oil)
Does not Evaporate
So, it leaves 15% by volume mineral oil behind.
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This would be my first choice, fixed many a NAD 3020 on/off switch with this:-
www.amazon.co.uk/Servisol-Super-Switch-Cleaner/dp/B000KEB6WW
Second choice WD40
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+1 on the Super Servisol recommendation. It might be a bit difficult to get hold of other than from someone like Radiospares (do they still exist?) though. I am lucky enough to know a stockist in Weston-super-Mare and bring back a tin every time I go to the UK so I now have quite a stock. It's made by a firm in Bridgwater called Ambersil and the email address for sales on the tin is sales.uk@crcind.com
Or maybe via www.ambersil.com
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Yes, Radio spares is still going, although it's called RS components now. It's a massive company selling absolutely everything, even in small quantities. Although they are expensive for many things.
Having said that, they've just started a swedish office. And with many things here being expensive they're pretty competitive on some stuff, plus they ship FOC next day. I can order stuff from them and get it quicker and sometimes cheaper (taking into account the free shipping) than i can from manufacturers agents here.
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This Stuff
www.lawson-his.co.uk/scripts/details.php?cat=Multipurpose%20Cleaners&product=1782
Ambersil Foaming Cleanser is great for equipment cases and covers, specially the ones with a crackled or non smooth finish, lifts dirt out.
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So it seems you want me to spend some money....mmmm, I need to give that one some thought.
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I was sure you had some WD40 knocking around!
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>> I was sure you had some WD40 knocking around!
>>
Oh yes, litres of it. The trouble is that there seems to be a little doubt about its efficacy.
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>> >> I was sure you had some WD40 knocking around!
>> >>
>>
>> Oh yes, litres of it. The trouble is that there seems to be a little
>> doubt about its efficacy.
>>
I'd say it's a reasonable strategy to try the WD40 first as it costs nowt, if that doesn't work blow 4 quid odd on the proper stuff.
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>> Yes, Radio spares is still going, although it's called RS components now. It's a massive
>> company selling absolutely everything, even in small quantities. Although they are expensive for many things.
>>
>>
I tend to use CPC these days on the rare occasions I need a few bits and can't get them off eBay.
cpc.farnell.com/
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>>This would be my first choice, fixed many a NAD 3020 on/off switch with this:->>
I still use my NAD 7030 tuner amplifier (3020 plus FM/AM tuner) and occasionally have to resort to cleaning the volume switch with one of the switch cleaners I have lying around in the shed.
But I find that turning the knob back and forth very quickly several times is equally effective. Obviously a common fault with the particular model, but even today (32 years old) it's a cracking amplifier..:-)
Last edited by: Stuartli on Fri 22 Apr 11 at 19:07
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>> >>This would be my first choice, fixed many a NAD 3020 on/off switch with this:->>
>>
>> I still use my NAD 7030 tuner amplifier (3020 plus FM/AM tuner) and occasionally have
>> to resort to cleaning the volume switch with one of the switch cleaners I have
>> lying around in the shed.
>>
I originally wanted to buy a 7030 (back in 1979) but they were out of stock, so I had one of the first 3020s. That was nicked when I'd had it about 8 years, replaced with a S/H Rotel RA840, that eventually went belly up on one channel, replaced with a Kenwood KA3020SE, which is still going.
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>>I originally wanted to buy a 7030 (back in 1979) but they were out of stock>>
It was 1979 when I bought the 7030 - still have all the reviews on it as well...:-)
30 watts per channel amplifier but 60 watts per channel output transistors. The saving on buying separate components (3020 and tuner) was quite marked.
It was also made to high standards in Japan, rather than the later NAD UK conceived products (New Acoustic Dimensions) which were sourced in Taiwan and similar manufacturing areas.
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>WD40 and a cotton bud to clean it.
The problem with using WD40 is that it leaves behind a residue that attracts even more carp. OK for a cheap temporary fix but proper contact cleaner is better - about £4 a can from RS or even Maplin.
If it's a well-used carbon track pot he may have no option but to replace it, they do wear out. Good news is that they're cheap and an old Grundig is worth repairing.
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a timely reminder
i had a sony radio cassette bought it in 1978 cost me a week wages + and over the years the pots went noisy,i used servisol as i had done for years but on this radio it dissolved all the plastic frame to the point everything including the poles for holding the dial strings collapsed
-www.recallsharp.ru/upload/iblock/6d1/6d1acec7a7ad474aec8eaede112fed3a.jpg
i came to the opinion servisol is only good for proper built old fashioned pots on proper boards so i would take what zero says on board very seriously
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>> If it's a well-used carbon track pot he may have no option but to replace it, they do wear out.
>> Good news is that they're cheap and an old Grundig is worth repairing.
>>
The bad news is sliding controls are likely to be expensive IF they are available.
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I haven't dared start yet. I will once the responses slow down or stop.
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>The bad news is sliding controls are likely to be expensive IF they are available.
They're readily available. Price varies on spec (as usual).
Everything from 89p at Maplin tinyurl.com/3jjrluj to tens of pounds for studio quality gear.
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Carbon tetrachloride was the traditional cleaner for crackly potentiometers.
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>> Carbon tetrachloride was the traditional cleaner for crackly potentiometers.
>>
>>>>>ooh i loved that smell when cleaning tyre casings up for a wee patch
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Yeah Trich. will give you a better hit and more efficient cleaning than Servisol (which is IPA based IIRC) but is also more likely to melt any plastic bits.
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They sell Carbon Tetrachloride in supermarkets in France for around €1 a litre bottle - I might wait until my next visit.
Last edited by: Dulwich Estate on Sun 24 Apr 11 at 23:47
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>> They sell Carbon Tetrachloride in supermarkets in France for around €1 a litre bottle -
>> I might wait until my next visit.
>>
Although we/I used to use the stuff by the pint for cleaning in the past, I'm pretty sure its use and sale is tightly regulated/controlled now...
And a quick google reveals this:
www.environment-agency.gov.uk/business/topics/pollution/34.aspx
While the French may sell you something that destroys the ozone layer, (or more likely a substitute which doesn't), I'd worry about the customs man stumbling across it.
(and the search which would follow).
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The French seem much more relaxed about selling such items in supermarkets.
They don't seem to have the nanny-state obsession which exists in the UK.
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I don't really think it's a nanny state that bans the sale of a chemical that can contribute to the destruction of the ozone layer and I personally doubt that you can buy tetrachlorure de carbone in French supermarkets.
It used to be used in fire extinguishers years ago but it produces WW1 phosgene gas when put on high temperature fires. Not really the stuff you want in your shed.
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Didn't they used to put it in old, brass fire extinguishers? IIRC it was dyed red to prevent it being used as a clothes, dry cleaning agent.
I was a passenger in a van that had one. We passed a car with an engine fire. Great I thought, I can have a go with an extinguisher. I unclipped it, but wasn't prepared for the speed of my driver, who grabbed it and squirted it all over the engine. It put the fire out but left everything a dark red. The car driver was quite ambivalent, pleased the fire was out, but asking how to remove the dye. We left without giving our details.
The paperwork we had to fill to explain why we'd used the extinguisher and get a replacement made me doubt if I'd ever be so helpful again.
Last edited by: bathtub tom {p} on Mon 25 Apr 11 at 11:24
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Our chemistry teacher used to use carbon tetrachloride to get chewing gum off our Barathea blazers and out of peoples hair...No longer have the blazer but the hair, while somewhat faded in colour is still there...
Last edited by: Humph D'Bout on Mon 25 Apr 11 at 11:53
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Our chemistry teacher used to use carbon tetrachloride to get chewing gum off
>>>.
>>>>>>> i used to use it on carpets
spray it on,let it freeze
then chip gum off with a toffee hammer
quite effective if used properly and obviously on commercial carpets rather than shag piles
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A toffee hammer ! I knew there was something missing from my household tool kit !
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dont forget your hammer through screwdrivers too
best thing ever invented for man :-)
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>> A toffee hammer ! I knew there was something missing from my household tool kit
>> !
A brilliant tool for 'tuning' bicycle spokes. Quite funny reading the concept of a toffee hammer being explained to the Dutch & Germans on the Brompton bikes yahoo group.
Last edited by: Bromptonaut on Mon 25 Apr 11 at 21:59
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IIRC, a favourite of car thieves for breaking a window, BIB?
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wouldnt have thought so
a screwdriver in the corner of the glass and twisted would be more effective
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Go to bed Bb, you've got work in the morning ;>)
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I always thought a fav for breaking windows was the automatic centre punch.
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Weren't some double glazed units supplied with a small hammer to break the glass in the event of fire?
The tip was to tap the glass in the corner, not the centre.
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Old Radio - Scratchy Volume Control - Zero
