Conductive boards again.

[TUBEDUDE]

Fiberglass / G-10

[Mark]

Fiberglass / G-10

It’s the way to go I’m sure.

[cmoore]

Fiberglass / G-10

Doesn't Mojo or Doug Hoffman make new boards for Fenders.?
If i were to pull all the components and wires off the fiber board for cleaning, I would just toss that board out and install a glass board as above.

[Mark]

Fiberglass / G-10

Doesn't Mojo or Doug Hoffman make new boards for Fenders.?
If i were to pull all the components and wires off the fiber board for cleaning, I would just toss that board out and install a glass board as above.

Hoffman make G10 boards and Mojotone makes fibreboards I heard that a maker of fibreboards had been selling fibre boards that were conductive from new. This has been my experience as well.

[dragonbat13]

I have the same issue with my 72 twin.

I plan on building my own board to try and retain the original circuit.

Mine isn't ultralinear, and for me the master volume is a plus.

Other than the pull boost, the master volume/ultra linear aspects of the amp are not the culprit of those amps being particularly sterile. If done correctly the master volume amps can be wonderful.

My amp sounded wonderful In the 90's when I first got it. Unfortunately I also learned a lot of what not to do.

The layout on these amps is close enough to an ab763 that I plan on making the adjustments accordingly.

I sure wish I had those blue drop paktron caps you have in there. Let me know if you want to get rid of them.

[Mark]

I was wondering if you turn your amp on and turn the tone controls on “5” (not really important), turn the volume all the way down, and turn the master all the way up. Then pull the boost switch on the master volume, do you get hum when the switch is pulled out and it stops when it’s pushed back in?

The tremolo/vibrato on the amp works but it is weak. With the intensity below “5” the tremolo effect is very weak. Is this what you encounter on your amp?

Here are some links from an Australian guy fixing two different SF Twin Reverb amps. He is quite thorough though I don’t know if I entirely agree with him on the diodes on the output stage.

https://youtu.be/7hODqQBca_0?si=OsN_vpWcWzqLdjTf

https://youtu.be/WZ8Mf9yvJS0?si=e8sPR1ejOWnvAj0h

[Mark]

Despite believing that Jelle is 100% correct about these boards, I have decided to see if Brad and Lyle’s advice has any merit on this board. I cleaned around one of the terminals and the voltage dropped around 10 volts, and I suspect the most improvement is gained from cleaning the top of board and there will not be much to be gained from cleaning the bottom.

I should have it back together in a couple of days and I will report my findings.

IMG_0323.jpeg

[Stephen1966]

Despite believing that Jelle is 100% correct about these boards, I have decided to see if Brad and Lyle’s advice has any merit on this board. I cleaned around one of the terminals and the voltage dropped around 10 volts, and I suspect the most improvement is gained from cleaning the top of board and there will not be much to be gained from cleaning the bottom.

I should have it back together in a couple of days and I will report my findings.

IMG_0323.jpeg

Yeah! I wouldn't mess around trying to restore these - time and energy could be better spent on just making fresh. However, the techniques Brad and Lyle use are worth some investigation... Brad's method involved dousing (paper) towels in IPA putting the boards between them in a sandwich - I think I would just try soaking the boards in a tank of IPA. Not sure paper towels doused in IPA as they were would have much if any capillary action. The other thing is to bake them around 80 degrees for a few hours. I can see how that might liberate any trapped water molecules in the fibres of the board. The top may be where the worst of it is but I guess you will run into problems like they did around the PI section of the board without depopulating it all first.

[Mark]

I had to try it to see if it would work. It sort of worked, which is to say there was a massive improvement to some areas and none to other areas. Ultimately, the best option would be to junk the board if I could. Unfortunately, the customer won’t have it. It’s not the cure all to conductive boards as some might think, chalk one up to Mr Welagen knowing his stuff.

https://youtu.be/sVaqv0LdhkI?si=AhZDTezFwRnNvWqD

https://youtu.be/7dr6XfCBVvE?si=bPOjeFdOxndR4H-p

[Stephen1966]

Good idea to shoot videos of your work. The customers always know best so charge accordingly.

Sounds like a "rinse and repeat" job.

[Mark]

I can’t say that I’m proud of this work, but I don’t know any other way of getting the parts off the board and yet they are secure. I would want to replace the board but the money isn’t there to do that.

IMG_0359.jpeg

This should be good for quite a few years, but it’s an ugly fix for the conductive board.

IMG_0361.jpeg

I will post more pictures. The amp is very quiet now and it sounds good apart from the tremolo which I think should have more intensity, I will have to look at. The thumping from the oscillator has disappeared entirely. I put that down to cleaning the board.

[Mark]

As promised here are a few more pictures.

IMG_0363.jpeg

The amp keeps giving me issue which I have to resolve.

IMG_0367.png

The other earth connection is similarly experiencing cracks. It’s ironic as I have never had this issue before and I checked the solder joint with a magnifying eye piece when the joint cooled.

IMG_0368.png

I will remove the solder, and refit the pots. I will tighten them fully and I will include braid when making the solder joint so it resists braking in the future.

The amp is very quiet and overall sounds pretty good, though there is a strange sound in the treble frequencies above high A on the 5th fret of the high E string.
The tremolo is dead quiet and operates okay, though it doesn’t do much below “5” on the intensity pot.

Thanks for your interest and input.

[rooster]

That's a lot of work that you've already invested Mark. I just saw this post, btw, and I've run into at least a dozen SF amps that had the problem you're experiencing. I have heard that high humidity was the reason that Fender began waxing the boards, FWIW.

Moving on, I watched the one video where the guy pulled a purple ruler out from under the board? Hm. Actually my fix experience somewhat follows this direction, however, perhaps the ruler wasn't a good idea. This said, my experience (in every case) was that the fishpaper beneath the surface board was the culprit. And this always occured when the amp had been worked over by some inexperienced amature repairman who elected to 'pour' on the solder to an eyelet. My experience - in every case - was that the conductive event was created when that lower board was burnt by the application of solder from the top board. Think about it, Fender did not solder the parts in place while the lower board was beneath it. It was always a virgin board (whether waxed or not) that went underneath the populated board. Typically, I would remove the old bottom board and replace it with either a fiberglass piece or a new blank Fender type board.

One way to test this potential cause, and what became my go-to direction, was to simply unscrew the top board and lift it off the bottom board and test the amp.

Too, FWIW, most of the problems I ran/run into were/are from the front end of the circuit, replaced parts in the tone stack basically, although I have run into super bad amature repair jobs where EVERY eyelet was buried in solder. Here, when this is the case, many times there were/are 'solder globs/balls' floating loose between the two boards - more reason to pull that bottom board.

[Mark]

Thanks for your reply Rooster. It certainly was a handful and the customer is very happy with the results. It’s his favourite amp again.

There were two spots where there was some minor conduction. I appreciate that the bottom board can conduct, but I figure if the bottom board has started then the top board could be in the same condition.

I figure that if you get the Garolite board in, then it’s the end of your problems.

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