Conductive fiber board, does location matter?

[Randall]

I am replacing the main and rectifier/bias supply board in a restore Fender that I know has been wet, probably for a while. I have just enough leftover grey non-conductive fiber material to do those two boards, but then there is the filter caps board. The caps are clipped out, but it still has resistors and jumpers. If I clip 375v on one of the 220K 1W resistors that is connected to a few other spots via jumpers, I get anyway from 0.6 v to 1.2 v depending on where I probe. So I ask, should I not worry and just use the original board since it's just a power supply board with no signals to interfere, pots to make scratchy or other mischief? I know that no conductance is ideal, but is 1 volt or so even a significant factor when working with HV? It's been under A/C for a week so it's nice and dry, and I realize it may act differently once it gets in a humid environment such as an outdoor summer gig here in SW FL.

Should I do the easy thing and just use this board, or do I need to find an alternative? I don't trust new black board (I had a real bad experience with it on a new build).

[Chuck H]

If you're out of board material then what I'm about to say is sort of like shutting the barn door after the horses are already out but for the future... When I lived in the San Jose, Ca. I had access to all sorts of industrial and prototyping shops. I went to a place that did G10 board material and asked after their biggest scraps. They had a piece that was about the size of a half sheet of plywood (48"X48" ish) that they sold me for $70. I've built over a dozen amps and a few replacement boards with that material and still have most of it. Totally worth the effort to find.

You can make circuit boards from a lot of materials. Pretty much anything heat resistant and non conductive. Ever look at innard shots of *umble amps? Some have wood grained Formica boards. Don't be afraid to get creative. I would sooner wait on a project than use a known conductive black board for any part of it.

[J M Fahey]

Try to get some epoxy-fiberglass material (G10?) and sleep like a baby.
As an alternative, don´t know in USA but here in Argentina you can go to any Electrical Supply shop, not where da´Mizzuz´ buys her desktop lamps but where Contractors buy electrical conduit, rolls of cable, etc. , here they always have available plates of thick (say around 1/8" , at least 1/16") brown phenolic paper boards (usually 3´ by 4´ or fractions of that) because they are a legally accepted base to build custom electrical distribution panels, when none off the shelf really suits you.
Inexpensive and good, I usually buy half a plate (2 ft by 3 ft) which lasts for years.
I normally make a dedicated PCB for anything I build, but sometimes I need a simple one-off, such as an auxiliary supply, or a crossover inside a cabinet, etc. and a 5 minute (literally) designed and built eyeletted board on phenolic paper saves the bacon and then some.



I am actually paranoid about fiberglass in any form (if it has to be cut/drilled/sanded that is) for good reason, so I prefer phenolic anything 1000 times

Absolute worst case (Saturday afternoon *urgent* job) you can always trust Formica

Anything but humid conductive fiberboard.

[Zozobra]

I'm a fan of PTFE board. I got a whole bunch of 3mm board on ebay for next to nothing. It is a dream to cut and drill compared to G10 or phenolic.

[Chuck H]

Doesn't PTFE put off toxic fumes when heated? But then, they use it for lead wire insulation too. Maybe just keep a canary near the bench so you know when to open a window and take a break

[Zozobra]

Probably, but I have so little time to work on things that my exposure is negligible. Clouds and silver linings I suppose.

[R.G.]

If the board is already clear of components, it would not hurt to put it in your kitchen oven at a really low setting, maybe 175F-200F and bake it out. This will remove any residual water that's just sitting there attached to the insides of the board. Can't hurt if you're looking at replacing it anyway.

[Thoriated Tungsten]

PTFE is perfectly harmless up to temperatures at around 350°C, where it starts to break down. Then you get Fluorine gas release... Hopefully you wouldn't see temperatures this high in an amp.

If it is all you have access to, then in a pinch it is possible to lift the copper foil off standard copper clad fiberglass board using a sharp hobby knife, solder and a large-ish soldering iron. Clean the board of flux residue afterwards using denatured alcohol, iso and/or water (whichever works for your flux).

[Randall]

I went with an 8" x 10" piece of clear Lexan from a home supply store for $4.50. I installed turrets, as my eyelets weren't deep enough. It works well, except you have to be careful with soldering heat, because it will soften and melt. I have almost all of it populated, and all looks well. Plus, it looks kinda cool with the original black backing board under it. Not my #1 choice for material, but it got it done with minor expense, and it looks good.

[The Dude]

And, it's affect on tonal properties will be very transparent.

[bob p]

This thread title should be non-conductive, right?

Lexan could be dangerous. It's not fireproof. For liability reasons I wouldn't ever consider building a tube amp that had a Lexan board in it, and there's NO WAY that I would ever sell one... but then Alexander Dumble reportedly sold amps with rosewood boards that were a fire hazard, and he made customers sign contracts that probably included liability waivers.

Garolyte #10 / 4-hour fire-resistant boards (G-10/FR-4) are the industry standard for a reason. They can be bought at reasonable prices from many amp supply houses. Most of them probably source it from McMaster-Carr in Chicago.

[bob p]

https://www.mcmaster.com/#grade-g-10-phenolic/=18ns7fc

[Randall]

I'm aware of the phenolic board options, and I've built on the G10/FR4 product and it is very good. But I'm trying to stay on budget with this project, I have no plans on selling these. I do not consider a well made Lexan turret board enclosed in a metal doghouse to be a fire hazard. I'm using the original fiber insulator board beneath it, with only ground jumpers running under the Lexan, so really, what's the fuss?

[Mick Bailey]

PTFE is perfectly harmless up to temperatures at around 350°C, where it starts to break down. Then you get Fluorine gas release... Hopefully you wouldn't see temperatures this high in an amp.

You get fluorine compounds - mainly carbon-fluorine based, but not fluorine gas under atmospheric conditions. Fluorine molecules are highly reactive and as the PTFE is dissociated through pyrolysis immediately form compounds with neighbouring molecules - mainly carbon, but also oxides as well as hydrogen (to form hydrofluoric acid). Some of the carbon-fluorine compounds were identified for military use as chemical weapons, such is their level of toxicity.

Fortunately, machining doesn't generate enough friction to be of concern. The main issue is particles that can be drawn through a lit cigarette and pyrolised, or drawn in through open heating sources such as propane or kerosene space heaters.

[SoulFetish]

I'm a fan of PTFE board. I got a whole bunch of 3mm board on ebay for next to nothing. It is a dream to cut and drill compared to G10 or phenolic.

I respect that! Getting PTFE anything for next to nothing is a rare find! I would love to use teflon in a number of applications, but it's so damn expensive to procure. Even the prices for relatively small sheets of PTFE from the suppliers I was looking at (when I was looking at board material) was crazy.
I wonder though, you have any issues stalking turrets of terminals in the boards? Teflon, is so resistant to friction, I wondered if anyone encountered terminals spinning or loosening in press fitting applications.