Pc board coating

[islandamp]

I replaced a couple of grid resistors on a B52 AT100 and had to scrape away some mild carbon tracks. The shiney copper, which is a ground plane, is within 1/2 millimeter of the 450volt B2 lug and resistor solder pads. Looks like it will definatly arc, to me. Is there anything to recoat the copper? Temporarily, I pulled one end of each grid resistor, twisted them, then soldered them to a male 1/4 spade, which I plugged into the female b2 connector. It is pulled up away from the board. Works fine but looks terrible.

[xtian]

Maybe you forgot to post your "after" photo?

Anyway, the product you're looking for is called conformal coating. E.g.:

http://www.amazon.com/Acrylic-Lacquer-C ... ating+419b

This stuff prevents corrosion, but I don't know about high voltage arcing. You'll have to read the data sheet. The blurb says, "It insulates against high-voltage arcing, shorts, and static discharges."

[xtian]

From their data sheet:

Dielectric Withstand Voltage >1500 V

Insulation Resistance 5x1012 Ω

[gingertube]

There are options for conformal coatings.
There is a "special" one which is specifically recommended for high voltage work, it is often labelled "Anti-Corona" or something similar, BUT this is probably an "overkill" for a tube amp. I use it in the day job to coat boards for a 2,500 Volt Photomultiplier tube power supply.
Cheers,
Ian

[islandamp]

I'll try that. I don't have an after pic, but while scraping the carbon, the blue coating scaped away and left alot of bare copper. I try not to mess with pc boards, but I was shocked at how close the copper ground plane was to the high voltage. Probably less than a millimeter.

[Stevem]

A Automotive liquid insulation tape is cheap, will take the heat and is all you should need voltage wise after two coats!

I myself use General Electric Glyptal Enamle paint only because I have it on hand for automotive block and head use as it is acid resistant also!

[JMFahey]

had to scrape away some mild carbon tracks. The shiney copper, which is a ground plane, is within 1/2 millimeter of the 450volt B2 lug and resistor solder pads. Looks like it will definatly arc, to me.

You bet.

Welcome to the joys of automated PCB design.

Of course it's Behringer's duty to check what the suppliers submit and ask for corrections, if needed (here?, definitely!!)

Here's some UL 60950-1 2nd Edition Tables suggestions for up to 300VAC .

Notice that in a tube amp with 450V on plates we are talking 450*0.7=315V if everything is fine, and peaks at least 50% above that if load is crazy impedance (such as a speaker and you are overdriving it):

[img:318:384]http://www.smps.us/chart.png[/img]

note minimum separation suggested is 1.5mm ... if both conductors are suspended in the air.

If there is any solid material joining them (where water can condense or lint/dust can deposit, both potentially current carriers) the minimum distande becomes 3.2mm

Less than a millimeter of PCB material?
What were they thinking?

[Kagliostro]

+ 1 for gingertube, the "anti-corona" spray is a good choice

K

[John_P_WI]

FYI only:

This is a popular one used in industry. We have soaked boards in bleach after they have been coated with this with no ill effect (to test the efficacy of the coating as bleach will immediately attack copper). Needs to be thinned with toluene to be sprayed.

http://www.ellsworth.com/products/confo ... -g-bottle/