gibson style tag boards conductive?

[imaradiostar]

I rescued a bunch of neat little tagboards from a Knight kit oscilloscope. They appear to be the same manufacture as the ones in many old Gibson amps, like this:



Whatever the case I've been trying to use them for simple builds and every time I use one instead of building a fresh turret or eyelet board I end up with strange problems- oscillation, DC on pots, etc.

Do these things tend to conduct like old black Fender boards?

jamie

[Chuck H]

Not in my experience. The reason the black boards conduct is that the black pigmentation is carbon. In fact ALL black pigmentation is made from carbon. If you charge it or heat it enough paths can form and you end up with a sort of carbon resistor. It's happened to me a bunch with the old black boards. So much that I won't even work on an amp that has one for fear that I'll end up replacing the board on my dime. But i've never had it happen on a 'not black' board. Perhaps you could try cleaning the boards with a strong solvent to remove any contamnates that could contain carbon. Ever notice the black stain on the wall above sconce lamps and old appliances. Just operating electronic stuff seems to out gas carbon. That's one reason old boards should be cleaned. I once did a paint job on a fire damaged building. The fire started because a regular flourescent fixture developed a carbon path between the contacts on one of the "tombstones" (those end sockets on four foot flourescent lamps) and ultimately dripped burning plastic onto a fabric covered chair lighting it on fire. So I suppose surface carbon can be an issue in old electronics. I say clean the boards and see if it helps.

Chuck

[Steve Conner]

I've had brown tagboards go conductive on me. As Chuck H says, might be worth cleaning them with a strong solvent like rubbing alcohol. Or then again, maybe moisture has got into the bulk of the board, and cleaning won't make a difference.

I only found out once the tagboard was fully assembled into my homebuilt amp, by which time I couldn't get it out to clean the underside. :-(

The offending board measured "infinity" on an ohm-meter. I think it takes a couple of hundred volts to break it down and make it start leaking.

[imaradiostar]

Thanks for the replies. I think in this particular circuit which is a very simple single ended amp I just built it poorly. I'd take pics and show you but I built it pretty lazily and it's embarrassing!

I'll try a few things before I make a new board. I think I just need to move some grounds around and shield one of the signal wires.

jamie

[Diablo]

I've read on the internet (so it must be true) that the tweed disease of conducting circuit boards is caused by humidity increasing the water content in the boards and that makes a conductive path. The cure is to then gently dry the board with a hair dryer. I don't know if any of this is true, but it sounds plausible.

[imaradiostar]

well...no luck so far.

I toyed with some grounds and bypassed various parts of the circuit but it just isn't playing nice. The circuit is mostly a gibson ga1rvt without trem or verb. When I designed it I thought I was being creative but it looks like it's been done before!

I'm going to try a new board with decent layout instead of my previous crapfest.

Why is it the simple stuff that ends up not being simple?

jamie

[cminor9]

I built a 6G3 using that black fiber board I bought (in bulk) before I knew better. I had weird problems too for a while, like sounds that would go away when I touched a lead of my tester to something. I got sloppy with the lead dress a bit, but even after I cleaned it up I had the same weird problems only less drastic. Found ways to work around the problems, but I wonder if the board had something to do with it? Another anecdote, but interesting correlation all the same.

Anyhow, I have gotten away from using those. Bought some glass epoxy turret boards. Easier to work with, very solid, and for a little extra money I know they'll be impervious to moisture problems.