Conformal coating or wax (or both)?

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CrazyFin
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Conformal coating or wax (or both)?

Post by CrazyFin » 16 Jan 2018, 13:53

I saw @lbcomms used some cool conformal coating when repairing a VCO block in the very interesting thread viewtopic.php?f=53&t=49419&p=438671&hil ... al#p438671
@lbcomms: As always, wonderful thread with lots of good and educational information and pictures! :clap:

I have sometimes used clean bee wax when I have removed wax from CB:s I have done repairs/mods in the VCO area but the conformal coating that @lbcomms used in the thread above is new to me.

I tried to google a bit but I am not sure what brand and type you are using?

I found something from MG Chemicals that seems to be what I am looking for:
https://www.mgchemicals.com/products/co ... -coatings/

The question is which of the different types is best suited for use in CB radio repairs, mods:
https://www.mgchemicals.com/products/co ... ating-419c
or this
https://www.mgchemicals.com/products/co ... ating-422b
Looks like the last one is more for high temperature environments though.

I was able to find a UK based webshop that sells MG Chemicals with ground transport to Sweden. I could not find a reseller in Sweden though.
http://www.circuitspecialists.eu/acryli ... ml-liquid/

Final question: Is this conformal coating a replacement for using wax or should I use both methods?

lbcomms
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Re: Conformal coating or wax (or both)?

Post by lbcomms » 16 Jan 2018, 19:34

We use Electrolube conformal coating, it can be had from RS or Farnell / Element 14 in both aerosol and liquid form.

We can't use beeswax, it melts on a hot day (we got 46 degrees here last week). A common repair here where radios have been imported from Europe / UK (the last one was a Stalker ST-9DX a few weeks ago) is replacing the internal speaker where wax from the VCO melts and drips into it, causing a big reduction in Rx audio.

It gets hot enough here to use a car as an oven...

https://www.youtube.com/watch?v=Og-t_74sQ78

CrazyFin
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Re: Conformal coating or wax (or both)?

Post by CrazyFin » 17 Jan 2018, 08:59

lbcomms wrote:
16 Jan 2018, 19:34
We use Electrolube conformal coating, it can be had from RS or Farnell / Element 14 in both aerosol and liquid form.
Ah, excellent. Thanks for the tip. Found it at RS now:
https://uk.rs-online.com/web/p/conforma ... s/3217324/


We can't use beeswax, it melts on a hot day (we got 46 degrees here last week). A common repair here where radios have been imported from Europe / UK (the last one was a Stalker ST-9DX a few weeks ago) is replacing the internal speaker where wax from the VCO melts and drips into it, causing a big reduction in Rx audio.
Ok so you are actually replacing all radios with beeswax to use acrylic conformal coating if you get a radio that has beeswax in the VCO and its surrounding area?


By the way, speaking of speaker replacements. I recall a really nice thread where you had a picture of you replacing an old paper element from a CB radio with a new and better ceramic element but I just cant find that thread... :roll: I've used the search function several times and I thought it was in that cool thread I linked to above where you rebuilt the Super Panther but I just cant find it. Do you recall this and if you do, what speaker element did you replace the old one with?


It gets hot enough here to use a car as an oven...
https://www.youtube.com/watch?v=Og-t_74sQ78
He he that is HOOOOT!! I can do hot dogs on my cars engine after a race... :D

lbcomms
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Re: Conformal coating or wax (or both)?

Post by lbcomms » 17 Jan 2018, 13:52

We just replace it as they come in for repair or on the odd occasion we buy and sell them. We've still got a nearly full box of speakers, when Hatadi (at one stage the biggest importer / seller of CB and ham gear in the country, most of it carrying their own brand name) went bust in the 90's we bought most of their spare parts stock at the liquidation auction. There were 3 or 4 boxes of internal speakers, probably so many because they had the same wax filled speaker issue we still see now, only they would have been dealing with warranty returns. Still got over 3/4 of a boxfull left.

Most of the old Oz legal radios would have had the wax replaced years ago, but we still see the problem when people privately import a radio and wonder why it goes very quiet after the first hot summers day in the car :D

Can't remember having ever re-coned a speaker. You must be thinking of someone elses handiwork.

CrazyFin
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Re: Conformal coating or wax (or both)?

Post by CrazyFin » 17 Jan 2018, 15:26

lbcomms wrote:
17 Jan 2018, 13:52
Can't remember having ever re-coned a speaker. You must be thinking of someone elses handiwork.
:oops: Hmm I was quite sure it was you and it was not about re-coning a speaker. It was a plain replacement of the whole speaker with a new and a better one. Anyway, I´ll keep on "googling"... 8)

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Re: Conformal coating or wax (or both)?

Post by CrazyFin » 17 Jan 2018, 16:08

Ha! Finally found it!
And yes, I was obiously totally messed up in my brains since it was indeed somewhere else and by someone else... Please accept my apologies Sue. :oops:

A really well looking restoration of a Hy-Gain 2795DX:
http://www.cbradiouk.com/2017/06/10/hy- ... n-by-pook/
( :shifty: My apologies if we are not allowed to post links to other forums but I hope this is ok since this is indeed a very interesting restoration example of a CB radio.)

Here is what I read there:
"Just got a new mylar diaphragm 5 watt speaker to replace the pathetic paper diaphragm, 0.2 watt piece of crap that was in it."
CB speaker - mylar element.jpg
CB speaker - mylar element - 2.jpg
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The Collector
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Re: Conformal coating or wax (or both)?

Post by The Collector » 17 Jan 2018, 18:01

I used to replace most of my old paper speakers with the mylar ones, simply as they sounded tinnier or higher-pitched. It helped somewhat, especially when mobile in noisy 80's cars.

lbcomms
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Re: Conformal coating or wax (or both)?

Post by lbcomms » 17 Jan 2018, 19:28

That was a nicely done restoration!

Some radios down here use that type of speaker, mostly sets for extreme environments such as boats and mining trucks. They are also used in some handheld business band radios.

Kaliphan
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Re: Conformal coating or wax (or both)?

Post by Kaliphan » 18 Jan 2018, 10:33

CrazyFin wrote:
17 Jan 2018, 16:08
Ha! Finally found it!
And yes, I was obiously totally messed up in my brains since it was indeed somewhere else and by someone else... Please accept my apologies Sue. :oops:

A really well looking restoration of a Hy-Gain 2795DX:
http://www.cbradiouk.com/2017/06/10/hy- ... n-by-pook/
( :shifty: My apologies if we are not allowed to post links to other forums but I hope this is ok since this is indeed a very interesting restoration example of a CB radio.)

Here is what I read there:
"Just got a new mylar diaphragm 5 watt speaker to replace the pathetic paper diaphragm, 0.2 watt piece of crap that was in it."
CB speaker - mylar element.jpg

CB speaker - mylar element - 2.jpg
You might want to consider getting a shielded magnet type instead of one that has a whopping big ferrite magnet around all those carefully tuned coils and transformers.

Or I might be talking out of my arse and saturating the coils with a permanent magnetic field will have no effect.

lbcomms
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Re: Conformal coating or wax (or both)?

Post by lbcomms » 18 Jan 2018, 11:43

A stationary (permanent) magnetic field will have no effect on the nearby circuitry. A large moving field (such as from a nearby unshielded mains transformer) will though, in that case a hum could be induced into the transmit and/or receive audio paths.

Kaliphan
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Re: Conformal coating or wax (or both)?

Post by Kaliphan » 22 Jan 2018, 10:30

Interesting, I agree a moving field is a bad idea, but surely if a low frequency magnetic field can affect a circuit wouldn't a static field also affect it with a more subtle 'fixed' effect that would show itself as detuning or altering the characteristics of an inductor based filter perhaps?

Could be an interesting experiment to prove or disprove it..

lbcomms
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Re: Conformal coating or wax (or both)?

Post by lbcomms » 22 Jan 2018, 14:03

Stationary magnetic lines of force will only affect it if the conditions are just right. When the current being carried by the wire (inside the component) changes, another magnetic field is created which reacts with the first, causing attraction or repulsion depending on the polarity. This movement then induces a voltage of opposite polarity into the wire. For this to happen, the wire has to physically move.

With high currents and very low frequencies it can be visible - try putting a few amps on an off (i.e. switching a high power 12V light bulb) connected to a thin wire going past one end of a strong permanent magnet. The wire will move in one direction when you energize the load, and the other direction when you turn it off.

A loudspeaker is another example. Feed it with 20V AC at say 1 KHz and it'll put out a loud tone and keep working, as the opposing current effect of the two fields will keep the heat to a minimum. But feed it with 20V DC and it'll soon burn out due to excessive current, because there is no physical movement.

There's no way a wire carrying a 10MHz or 27MHz signal can mechanically move that fast, due to the inertia of the wire material. Because there is no relative movement, the signal at that frequency won't be affected by a static magnetic field.

In practice, magnetism is a bit more complex than that 5 minute explanation. Plenty of further information out there, along with a fair wad of misinformation (i.e. overunity / perpetual motion machine / fuel saving gadgets) scams too...

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