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General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
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20th Jun 2022, 8:48 pm | #1 |
Pentode
Join Date: Mar 2008
Location: Bury, Lancashire, UK.
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Advice needed with mains dropper
Hi all
Half of this dropped has lost its insulation flaking off due to age and heat,any idea what was used ? would shellac be ok to re cover it or am i likely to start a fire? it's ok left nude I just thought cosmetically it would look better.regards Keith |
20th Jun 2022, 8:57 pm | #2 |
Dekatron
Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 5,763
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Re: Advice needed with mains dropper
Crikey no - not shellac.
If you want to spray it with anything, I'd suggest matt black stove paint, which is good to 600C - way above the temperature your dropper is likely to attain. EG, something like this: https://www.yorkshiretrading.com/pro...CABEgL1oPD_BwE Ride at your own risk!
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20th Jun 2022, 9:53 pm | #3 |
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Re: Advice needed with mains dropper
That looks very dodgy and may contain asbestos.
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21st Jun 2022, 7:49 pm | #4 |
Dekatron
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Location: Newcastle upon Tyne, Tyne & Wear, UK.
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Re: Advice needed with mains dropper
Car engine enamel or brake drum paint should do.
It looks like the original was some sort of paint, I doubt it was asbestos on that design of dropper Ed |
21st Jun 2022, 8:08 pm | #5 |
Pentode
Join Date: Mar 2008
Location: Bury, Lancashire, UK.
Posts: 138
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Re: Advice needed with mains dropper
Hi
Thanks for the replies. ok Dave no shelac I did wonder !no asbestos it's a plain old ceramic tube the stove enamel is the way to go then.the devil in me was kind of looking forward to the Roman candle \shellac shed warmer !! Regards Keith |
21st Jun 2022, 9:00 pm | #6 |
Pentode
Join Date: Jul 2007
Location: London, UK.
Posts: 165
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Re: Advice needed with mains dropper
I have used, to great success, TECHNICQLL HIGH TEMPERATURE SILICATE 1200°C. It is a grey paste in a 70ml tube it can be thinned down with water and painted on with a brush and air dried a couple of coats is normally enough.
Colin |
22nd Jun 2022, 6:55 pm | #7 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
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Re: Advice needed with mains dropper
I would leave it nude; any sort of paint/coating will only reduce its ability to dissipate heat.
But equally I'd investigate why the original coating has been so comprehensively vapourised. What's it from? Has something downstream of the dropper gone horribly low-resistance perhaps? Ot has it been fed with 250V when set to 120V ?
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22nd Jun 2022, 11:37 pm | #8 |
Dekatron
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Re: Advice needed with mains dropper
What prevents the turns of nicrome wire from touching each other and reducing the resistance?
Presumably the paint.
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23rd Jun 2022, 6:54 pm | #9 | |
Nonode
Join Date: Jan 2010
Location: North Somerset, UK.
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Re: Advice needed with mains dropper
Quote:
If making NEW high power resistors from new and shiny nichrome wire I have been known to pre-oxidise it by running it at a bright orange heat. A vehicle battery or the mains supply may be used according to the voltage and current needed. Take care. |
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23rd Jun 2022, 9:05 pm | #10 |
Pentode
Join Date: Mar 2008
Location: Bury, Lancashire, UK.
Posts: 138
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Re: Advice needed with mains dropper
Hi again
Interesting thoughts on the dropper its in my HMV 1115 1946 era so getting on a bit ,the end with the coating still on is the cooler end across the dial lamps I may just leave it as is ,strange though the 3amp fuse had blown in the plug and dial lamps o/c even though the mains tapping was set to the correct point no shorts have been found .Also the mains switch was high resistance now ok after a strip down and contacts cleaned and 're faced ,rather oddly the single pole is in the neutral lead ,The usual wax caps have been replaced and one 100 K ,the set is on the bench and working fine after osc and ae alignment.Keith |
24th Jun 2022, 8:33 am | #11 |
Dekatron
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Location: W.Butterwick, near Doncaster UK.
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Re: Advice needed with mains dropper
It could be porcelain or asbestos looking at that dropper. Thankfully easy to tell though.
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24th Jun 2022, 10:54 am | #12 |
Heptode
Join Date: May 2010
Location: Warminster, Wiltshire, UK.
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Re: Advice needed with mains dropper
Does it have to have insulation. As long as the resistance wire doesn’t sag I would leave it. Lots of my old Ekco radio have bare droppers Andy
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24th Jun 2022, 11:01 am | #13 |
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Re: Advice needed with mains dropper
Got to say I agree with Andy.
Despite the loss of the coating it looks to be in good condition so if it works just leave it alone. You can check the resistance to make sure there are no shorts. Its part of the life of the set Cheers Mike T
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24th Jun 2022, 7:35 pm | #14 |
Pentode
Join Date: Mar 2008
Location: Bury, Lancashire, UK.
Posts: 138
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Re: Advice needed with mains dropper
Hi
It's definitely a ceramic dropped ,although the set works there is a 2300pf cap (c19) on the circuit diagram that if it went s/c it would short out the top three sections which are the mains tapping,s so may be that would account for the burnt off paint it looks like a wax covered mica, as for the dial lamps after closed inspection I think they failed due to age no vaporized filament just a small disc in the centre,so c19 will be replaced as a precaution also all rubber wire has been replaced and the wiring to the dropper replaced with silicon type.Not a pretty set with its green painted front but it's growing on me and saved from the skip.regards Keith. |