Fender Amps - Circuit Board Conductance

[Gibsonman63]

I live in a fairly humid environment. I haven't had any issues with Fender's circuit boards, but all of my amps are stored in an air conditioned room.

I restored a BF Fender Twin a couple of years ago that had gotten really wet and been stored in a garage for a long time. I had a few months of tinkering with it and a lot of cosmetic work, but I didn't replace much on the boards other than the electrolytic caps. I got it working with no fiber board issues. I would suspect that if you stored one of these in a dry enough environment for long enough, any moisture in the fiber board would eventually evaporate.

[Structo]

I have wondered before how much Moj0 is from that circuit board being slightly conductive?

Just like a guitar an amp is a sum of it's parts.
When they all come together just right, you can have an exceptional amp.

[ElectronAvalanche]

Hi guys,

interesting discussion. I remeber that I read somewhere that the conductivity of the board is indeed supposed to be part of the mojo as Tom stated. OTOH there are many amps out there that sound fantastic without a conductive eyeletboard?!?

Since the amp is a Fender clone and thus not a real vintage amp I have decided to rework the amp and to replace all boards with epoxy boards. I will even go so far and do my own printed circuit ala Dumble (sort of a semi printed circuit).

Some things I can not live with due to the conductivity of the boards:

*ticking vibrato (even lifiting the trem roach from the board does not help too much, the Vibrato is per se non-ticking as Dumble prove in his Dumbleland / SSS). Ticking gets worse with higher humidity

* DC on the Reverb pot due to conductivity (scratchy Reverb pot, the pot is ok btw, I swapped in a new one and it too was scratchy)

I will post some before and after pics.

Cheers,

Electron

[frankeg]

I just ran into this problem. See "Problem with1966 Super Reverb" post. I live in Pennsylvania and the amp I'm working on was stored in an unheated garage for several years. The board has a couple of waves in it with both ends raised up. I have several tube amp books and a few of them mention the conductive board issue. If I remember correctly, Dave Funk's tube amp book has a write up on the problem. It is primarily a problem in high humidity areas and depends on how the amp is used/stored.

[Mark]

It’s an old thread but conductive circuit cards happens. How much it affects your amp depends where the moisture it. I have tried removing all the components off the board and putting it in an oven (used for electronics fault finding) for a good eight hours and I couldn’t get the moisture out of the board. As far as I’m concerned a Garolite board is the answer.

[bepone]

just buy the new reissue fibre board , paint with plastic spray, and transfer all the components there, in a few days there will be a new amp

[maxkracht]

It is very humid here in the summers and I definitely see some board conductivity problems. It's not insanely common, but not uncommon. Usually it only matters in places where the eyelets are too close together or close to a mounting screw. Some amps have the input grid stoppers right next to the preamp power supply node and it will leak enough that your guitar's volume will be scratchy with DC. It is always a measurable thing, meter probe connected directly to the board.

The waxed boards were supposed to help, but often make things worse, collecting dirt, dust, nicotine, and flux... I usually scrape as much wax as possible, melt the remaining wax with a small heatgun and clean with paper towels/cotton swabs. The backerboard can cause problems too, sometimes you will see holes burned through one and the carbon traces are even more conductive. If I suspect this, pull out the back board, scrape off carbon, wash, soak in IPA, then let all of the alcohol evaporate, scrub off any remaining dirt, repeat or reinstall. Rarely it needs a completely new backer board.

For smaller problems on the main board, cycles of heat/IPA/time usually work. Sometimes you need to remove components to avoid the alcohol removing lettering, or avoiding overheating them, but often you can get away with metal shield/kapton and fix a trouble area. I don't think it is the moisture itself that causes problems, it is moisture and conductive dirt/salt/etc. so once things are adequately clean, it should be fine for a good while. Overheat a noisy old CC resistor and you can often see what looks like flux bubbling out the end. Haven't tried it, but I'm guessing putting those in the oven slowly gets rid of enough of that gunk, then shellac to seal it.

Parts placement definitely has something to do with how an amp sounds, but leaky board doesn't add to mojo in my opinion. People just like to justify old materials and sell amps that use them at a premium. I have some bumblebee caps with a lot of "mojo" that I could sell if anyone is interested.

[FUCHSAUDIO]

I recently restored a '66 Vibroverb that had seen water. There was rust under the board when I lifted it, even under the filter caps. There was DC all over the place....
I ended up buying a Hoffman board (which is fiberglass, FR-4 I think), and transferred the important parts over, and replaced out of spec and non-salvageable parts with new.
The layout of the rivets was exactly what I took out, so it matched the amp and the Fender layout perfectly !

It sounded great and no more conductivity. I highly recommend it as an excellent solution.

[Mark]

An exact fit is what I’m looking for. The fibreglass boards are great. Thanks for your input Andy.