Protecting a circuit - ideas

[Will777]

Hi,

I have a FM transmitter circuit with exposed air wound coils - I have seen some ppl put a substance inside and over the coil to protect it - I've tried in vain to find out what this is - is it silicone sealer?

 

[(*steve*)]

Why does it need protecting?

 

[Will777]

Why does it need protecting?

The coil determines the frequency - so I don't want the coil to bend and change the frequency. Handling the PCB sometimes will bend the coil.

Like this:

Note the coils - is this silicone sealer?

 

[(*steve*)]

no idea, but adding this stuff will probably affect the operation of the device -- it may just require retuning, but you never know.

Then again, considering how this has been built, I guess there's quite some leeway...

 

[Will777]

This is a sample of a bird's nest design I found on the internet try and show what I'm looking for - I built a kit on a PCB.

 

[LTX71CM]

To me it always appeared to be a cardboard tube with wax holding it all together.

 

[Will777]

Cardboard? Inside the coil? Not sure if I see that?

 

[LTX71CM]

Not in your example picture, in the radios I've taken apart throughout the years. Your photo appears to be hot glue or an epoxy.

 

[Will777]

Aah, I misunderstood.

Cool - that is one idea. I suppose since the epoxy does not conduct it will be ok to fill the coil with that.

Thanks!

 

[Will777]

I tracked down a very old post on another forum that confirms that hot glue works well - if anyone else has this same problem

 

[Zander]

Why does it need protecting?

A short between the coils maybe.

Where do you get those variable capacitors? I can't find them on mouser.

 

[NickS]

I use hot glue regularly for dead bugging but when it goes on conductive areas we prefer DOW 3145 RTV because the circuit doesn't have to get very warm before the hot glue starts to run(among other reasons).

 

[Laplace]

The old standby coil coating is GC Electronics Polystyrene Q Dope.

http://www.gcelectronics.com/order/SubCatPDF/thinners Solvents Coatings 55-56.pdf

 

[Will777]

Where do you get those variable capacitors? I can't find them on mouser.

I live in South Africa, so I know of one or two suppliers here that stock them.

http://shop.rabtron.co.za/catalog/a...Csid=ad6297bf458880b05b5c3729ae0cc4db&x=0&y=0

I struggle to get the capacitance values I need though

 

[Will777]

Thanks for the other two suggestions, will have to see what I can source locally as importing tends to be too expensive