Fiberboard(I'll never use it again)

[jeff]

 I recently dusted off an amp that I build last winter that I hadn't played in a while. Sounded great. I noticed that when I turned down my volume on my guitar it sounded scratchy. I thought DC, so I tested for DC on the guitar cable. Sure enough there was .18V on the cable. This is the second amp that I've build using fiberboard and gotten stray voltages. The input goes to a 68K resistor that is mounted on the board. When I remove the resistor and wires and measure the empty eyelet there's voltage, on the empty eyelet. There is no flash on the other side of the board, it's leaking through the board. When I built the amp I checked all the voltages and there was no problem with the input. I've heard of this happening to amps that have been stored in the basement but I have always stored my amp in my room, not in a damp basement where the fiberboard could suck up moisture. I don't know if this happens with all fiber board, I bought some cheap crap, or this was a bad batch but having to completely rewire another amp is a drag. I'm done.

That's my experience, take it for what it's worth. Beware fiberboard.

[bluesbear]

The only thing fiberboard is good for is in restoration work... and I don't like it even then!
Dave

[Leevi]

Do you mean this type of board?

http://taweber.powweb.com/store/fb-v.jpg

/Leevi

[tubenit]

Leevi,

You posted a picture of a tagboard. That's not made from fiberboard. Fiberboard is like the stuff old Fender amps used.

with respect, Tubenit

[Geezer]

Like this.....




it's like the original paper based stuff Fender used in the 50's/60's....known for gathering moisture, becoming conductive & warping

[Leevi]

You posted a picture of a tagboard

That's good since I almost always use the tagboards in my amps.
/Leevi

[phsyconoodler]

Never had any problems with fibreboards in any amp I've used them in.I have had problems with silver mica capacitors that make you believe it's the fibreboard that's causing the issues.
  I've seen one bad fibreboard in a 1964 Fender Deluxe. One.

[bigsbybender]

The Fiberboard is less reliable in moist or humid climates. 

Psychonoodler, we're too far north and west to have major problems with that. I have noted some Fenders that have spent their lives in basements that have had weird noises probably less than 5 out of hundreds. When I put them in a dry place for a period of time, the problems go away.

Doug developed his board system in Florida, where this is a major problems with Fender amps.


j.

[jojokeo]

Wasn't it Doug that has info for isolating the board w/ some insulating-type washers under the board for this kind of problem as it relates to a grounding issue?

[Cathode_ray]

Seen a lotta Fender amps in South Carolina... Never had this issue. And it's pretty humid - especially in the lowcountry. "Spect the heat of playing keeps them dried out. Not saying this isn't an issue because it will cause issues with condenser mics. But they dry with use as well.
Is prolonged storage, perhaps in a cool and/or damp environment most of this issue? And should we get in the habit of drying 'em out after any prolonged downtime?  I'd really liketo know...

[jojokeo]

Fact of the matter is that if it's an actual problem, it will be again at some point even after drying out. It will eventually just get re-humidified again at some point kind of like a ticking time bomb. But, the severity can be minor and an annoyance like scratchy pots or worse if it's really bad.

[sluckey]

Here's a typical conductive board problem. There was a resistance reading between the eylets that the trem roach normally connected to. The symptom was a ticking problem from the tremolo circuit.  Hanging the parts in the air, is a quick fix for a conductive board between the eyelets.

[jeff]

Even if that fixes the trem problem what else is going on in the amp? I imagine you'd have some type of feedback going on between every other part of the amp, where a little signal is getting where it's not supposed to be.

I was first thinking of putting a cap between the input and the grid of the first tube. That will solve the problem of having DC on the pickups, But, If theres DC on the grid, that's throwing off the bias of the tube. Plus is it going to get worse and worse? And what else is being thrown off?

I want to replace the board, but all my parts leads are cut to length to fit the eyelets of the board. I like the turrets that Doug sells but I don't think I have long enough leads to wrap them around to use them. I don't want to have to buy all new caps and resistors. Any suggestions what to use as a replacement board? I think Doug's board is too thick to use with eyelets.

It's a pain because I did such a good, clean job of wiring this one up. I just hate it when you do everything right and it still comes out wrong because of something stupid like a bad part.

[sluckey]

That was just an example of conductive flypaper board. There are probably a lot of old amps out there that have small nuisance problems or just don't sound right and nobody can seem to fix them. Many may just have slightly conductive boards. The boards may only be conductive in certain areas and fine in other areas. The possibilities for problems are probably infinite.

This is just a hobby for me and I don't fix amps for people. I would never use the stuff in anything I build. I trust fiberglass.

[John]

Jeff, Doug sells tall eyelets that fit his 1/8" board. Also, a lot of guys use the turrets the same as eyelets, just bend the leads and drop them in the center hole. Hope this helps.
Page where all that stuff is listed.
http://www.hoffmanamps.com/MyStore/catalog/parts12.htm

* EL34 I fixed the link

[PRR]

> there's voltage, on the empty eyelet.
> Sounded great.

So what is the problem?

Is the pot-scratch unbearable? Play Louder!

With modern high-impedance voltmeters, it isn't odd to find small stray voltages on dis-connected nodes. For electrometer work, best-fiberglass isn't good enough, But for audio amps, we don't hear DC (maybe while turning a pot) and circuit impedances are never extreme.

[jeff]

I'm worried about .18V on my pickups.

[phsyconoodler]

Are the pots on your guitar noisy?Yes,you have an issue. No? You don't have an issue.

[jojokeo]

With modern high-impedance voltmeters, it isn't odd to find small stray voltages on dis-connected nodes. For electrometer work, best-fiberglass isn't good enough, But for audio amps, we don't hear DC (maybe while turning a pot) and circuit impedances are never extreme.

I've come across many situations (through my work) where w/my high-z VOM I've measured voltages (albeit AC for this issue) where you get what I call "ghost voltage" on components and wire paths. Once a small load is put on it, then the voltages disapper and there's virtually no current to go along w/ the ghost voltage. So really what you're seeing is something that's not really there, it just appears to be. Hence my term for it.

[G._Hoffman]

I'm worried about .18V on my pickups.

Why?  That is very small. 

Now, if you were measuring 1.8V, you might have a problem, or if you were using a transistor amp, but tubes are pretty forgiving about precise voltages.

Are the pots on your guitar noisy?Yes,you have an issue. No? You don't have an issue.

What he said.


Gabriel

[jeff]

Doug does have eyelets for his fiberglass boards! I thought I checked before and thought he only sold turrets or short eyelets for fiberboard, now I see he sell tall eyelets. Yeah! I thought I was screwed if I had to use turrets because the pots are kinda close to the board and with turrets I wouldn't be able to remove the pots without removing the board.

Anyone work with his board, Is it hard to cut? What do you use?

Here's a picture you can see how the fiberboard swelled up(maybe hard to tell from pic but it's buckled like a arch under filter caps). It was totally flat when I built it. Like I said It was always kept in my room not in a moist area. Maybe it's not all boards just a bad batch. I got these boards form Mojo.

[stingray_65]

Doug does have eyelets for his fiberglass boards! I thought I checked before and thought he only sold turrets or short eyelets for fiberboard, now I see he sell tall eyelets. Yeah! I thought I was screwed if I had to use turrets because the pots are kinda close to the board and with turrets I wouldn't be able to remove the pots without removing the board.

Anyone work with his board, Is it hard to cut? What do you use?

Here's a picture you can see how the fiberboard swelled up(maybe hard to tell from pic but it's buckled like a arch under filter caps). It was totally flat when I built it. Like I said It was always kept in my room not in a moist area. Maybe it's not all boards just a bad batch. I got these boards form Mojo.

Yeah I use the stuff from Doug a lot.

Like Doug, I use it for lots of things besides circuit boards too.

You can cut it with just about anything, band saw, table saw, hack saw, Dremmel etc.

It is abrasive to cut and machine, but you would really only worry about that in a production environment, making a board or two a month, you won't notice at all. Use a standard black jobber drill for the holes, might be worth having 2 drill bits just in case, I hate sharpening bits smaller than 3/16, my eyes aren't what they used to be.

Setting eyelets or turrets is more tedious than it is difficult. It is only recently that I've eased up a LOT on the force I use to set them. Made a world of difference in the constancy of the flare for the better.

I will also go through after and check for loose terminals by tapping the whole board on its side on the table. Loose eyelets an turrets will rattle or buzz. This is not necessary at all because when you solder a component on they cease to move, its just my OCD.

A useful trick I found was to use a dry erase marker and color the whole board and lay out the holes. After you center punch your scribe lines, wipe off the dry erase and it will fill the small detent the center punch made making them easier to see (poor eyesight remember!)

[John]

Jeff, to cut the board I used first, a jigsaw with fine tooth blade, and second time a circular saw. Either one works fine, but the jigsaw gives you WAY less dust.

[TubeGeek]

I have used Doug's boards...I cut them down to size with a jigsaw and a fiberglass cutting blade.  Works nicely.  I've made turret boards and eyelet boards, both turned out good.

[tubenit]

I use a hacksaw and it cuts very quickly.

Tubenit

[LooseChange]

I use a hacksaw and it cuts very quickly.
Tubenit

I'm a hacker too.

[John]

Youse guys are so old school! 

[EL34]

I have seen many a Fender that flowed current through the fiber board.
Especially in the areas where a high voltage eyelet was close to another eyelt of lower potential.

I have done the "suspend the parts in mid air" trick lots of times on Fenders.

Me likes glass epoxy board