What is the goop used to hold down parts?

[HarryB]

What is the goop used to hold parts down in circuit board amps? It looks like hot glue, but with tube heat I can't imagine that is what it is. Is there something 'off the shelf' (of a hardware store for instance) that can be used to hold down parts to a circuit board? Thanks for your help.

[Wakarusa]

Silicone.

[HarryB]

Thanks Todd. Is there a silicon product that you have used for gluing parts down that withstands heat and high voltage? I have a circuit board where burned screen grid resistors took out the circuit traces. The goop would secure the new wire and new resistors.

[Wakarusa]

You asked what the stuff was that you typically see used -- whether I'd use it is a different kettle of fish :)

I'd think most any 100% silicone adhesive would do (available at any hardware store), but for your application I'd be wary. It's a lot more common to see this stuff used to glue down big electrolytic capacitors to reduce mechanical stress on the leads (so it isn't just the leads supporting the heavy component). Even then, I've seen cases where the stuff gets hot and runs (PV Classic 30/50 suffer from this pretty often). Another thing to be mindful of -- silicone has capacitance. If you inadvertently bridge connections with this crap it can lead to cross-talk, undesired frequency shaping, or even oscillation.

I have never bothered to glue down a wire used to replace a burned/damaged PCB trace -- just soldered it to the available pads/leads and let it go (maybe a tie wrap or two if the new wire is long). If the pads are gone I'll usually go off board with a terminal strip. For things like screen resistors that really ought to have an air gap between the body and board securing them is a problem -- I doubt that silicone is a good long term solution (hrmm.. hi temp gasket sealant intended for automotive use maybe?).

Anyhow, in your case I'd probably try to relocate the screen resistors to the tube sockets if there's anything you can solder/mount to there.

[Reinhardt Amps]

silicone will actually retain moisture and go to hell over time. it will actually make metal rust.
Use "goop" i think its called amazing goop or some shit at most any store (lowes,walmart,home depot, etc) its a lot tougher than silicone, and dries clear. Ive used it to glue a few things down from time to time.

[HarryB]

Yeah, usually I can just solder the replacement wire to what's left of the old trace and be done with it. This could end up being a longer run. I wanted to minimize vibration related stresses. I will look at the board again though after what you suggested about external mounting.

I may try that 'amazing goop' Bob, thanks. If I don't use it on this job, it will certainly work on those crappy little solid-state kid amps that sometimes find their way to my workbench. :)

[HarryB]

Oh Bob, I was reading on the MG Chemicals website while looking for a product. The corrosion seems to be from the curing process. They do have a silicone based product that doesn't corrode RTV6708.

[NitroLiq]

http://www.a1fakhrisupply.com/catalog/GOOP14021.jpg

[phsyconoodler]

They sell some stuff at electronics shops that gets harder than silicone and it's specifically for electronics work.
RTV automotive silicone does NOT absorb moisture and does NOT corrode metal parts.And it will hold forever if the surfaces are clean.

[ClinchFX]

Another adhesive that was used on VCR boards, to hold down production mod components is a cream coloured goop. The problem is that, with age and heat, it goes dark brown and conductive. In the 80s I fixed a heap of VCRs just by removing this stuff. The VJ has this glue on the PCB, as does a lot of other electronics gear from China. I recommend scraping it off and replacing it with "Neutral Cure" silicone, which doesn't release corrosive substances as it cures.

The only "contact" type of adhesives I ever use in electronics is the stuff that dries clear, but I never use it on the PCB or components. The yellow or brown glues will often become conductive as they age.

Peter.