Conductive boards again.

[Mark]

I have a silver face Twin on the bench and I have never seen a board like it. The board is stuffed.

When I got the amp the power transformer was stuffed, I noticed that the tone control caps are soldered on one side

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[Mark]

Purely for interest sake here is a picture of tagstrip being used to eliminate problems with a conductive board at the Fender factory.

They knew about the problem in the silver face amp days.

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[Stephen1966]

I admit I am curious... Are you even going to try to resurrect this beast?

How do you even begin to evaluate whether an amp like this is worth saving? And to what lengths you might go to preserve the legacy value of the original?

[ampdan]

What makes you believe that tag strip is original? Out of hundreds(thousands?) of Fender amps I've seen, I have never seen that.
There's a lot that looks "not factory" in that amp.

[Mark]

I never seen a Fender with these lugs before either but it is what it is.

The lugs are original as the resistor attached to the lugs is the very same type as is used on the other side of the P.I. grid. There are no signs of the resistor being removed and resoldered.
The solder joints are untouched and the wax coating is still on that part of the board. Have a good look at the picture.

Why do you think it’s not original?

[Mark]

I admit I am curious... Are you even going to try to resurrect this beast?

How do you even begin to evaluate whether an amp like this is worth saving? And to what lengths you might go to preserve the legacy value of the original?

Yes, I want to save the amp, I don’t know what it will take to get it working properly. There is the thought of turning it into an AB763 amp. The push/pull master volume with switch is a bit of a pain.

[Stephen1966]

I admit I am curious... Are you even going to try to resurrect this beast?

How do you even begin to evaluate whether an amp like this is worth saving? And to what lengths you might go to preserve the legacy value of the original?

Yes, I want to save the amp, I don’t know what it will take to get it working properly. There is the thought of turning it into an AB763 amp. The push/pull master volume with switch is a bit of a pain.

Great to hear! If you aren't going for a faithful restoration then I bet there's much you can do to transform it into something special... something Ultra Phonix (ish)?

[angelodp]

Perhaps you have seen what Psionic (Lyle) goes through with this issue. An alcohol lavage and meticulous removal of the residue that builds up on the wax boards can be quite effective. Then there is the under board that gets polluted. I have pulled that board out on my silver face champ and done the whole lavage with alcohol and it does work to eliminate the DC that gets on those old boards. It's a process but then you have a great fender amp again. Long live old amps.

[maxkracht]

One caveat with the scrubbing, heating, alcohol method; I have seen a few where the backer board gets charred. Sometimes you can lift the top board slightly and pull the backer board out without disassembling everything, then scrape off the carbon, add some fish paper, etc., or just replace the board. Sometimes the last guy pooled too much solder under the board trying to figure out the conductive board problem and made everything worse...

[Stephen1966]

You have a nice collection of carbon comp resistors there and though it looks like the boards are the real problem here was an interesting commentary on reconditioning the carbon resistors from Hi Fi Collective:

Being made of organic material, they do have the tendency to absorb water from the atmosphere. This absorption can increase the actual resistance of the component, hence the slightly higher-than-normal tolerance published on this page. To fix this, remove the water from the component and seal it. The best method is to place the resistor/s on a baking tray, set your oven to 80 degrees centigrade and leave it in the oven for 8 hours. The secret is to remove the moisture slowly. If you rush, it will become noisy in the circuit. Once cooked, seal the body of the component in Shellack (preferably the flakes) to stop further water absorption. At the end of this procedure, you will have much lower noise and more closely tolerant resistors.

https://www.hificollective.co.uk/compon ... stors.html

Honestly, if this were mine I wouldn't bother with reconditioning the boards - a lot less hassle and peace of mind to just make new ones - but here were a couple of fun videos that seem up your street




There are a couple more videos after these...

[jelle]

Mark, with 20-30VDC on the board, I can tell you that there is no saving this board. Its something i have tried several times....take board out, take all parts off, remove paraffin with heat gun/paper towels, acetone/brake cleaner clean off the residual mess, rebuild.... Then the same thing happened when all was done. its time for a new board.

[Mark]

Mark, with 20-30VDC on the board, I can tell you that there is no saving this board. Its something i have tried several times....take board out, take all parts off, remove paraffin with heat gun/paper towels, acetone/brake cleaner clean off the residual mess, rebuild.... Then the same thing happened when all was done. its time for a new board.

Good to hear from you again. It’s been too long. Thanks for answering my post.
I have been down the path before as you know, I have cleaned boards with MEK and alcohol to no avail. I have had boards in an oven for 8 hours in order to remove moisture. Once they are conductive there is little chance of going back.

[Mark]

Perhaps you have seen what Psionic (Lyle) goes through with this issue. An alcohol lavage and meticulous removal of the residue that builds up on the wax boards can be quite effective. Then there is the under board that gets polluted. I have pulled that board out on my silver face champ and done the whole lavage with alcohol and it does work to eliminate the DC that gets on those old boards. It's a process but then you have a great fender amp again. Long live old amps.

I haven’t seen Lyle’s video. He does have good content so I will check it out.
As I mentioned to Jelle, the circuit card in my Bandmaster is conductive. I removed all the components from the board cleaned the muck of with MEK and washed it in alcohol. I then had it in an oven (low temp) for 8 hours and it still had the same problem. I even bought a new circuit card on eBay and it was worse than my circuit card. The damn things need to be tested with a megger.

This current board in the Twin is worse than my board.

[Mark]

You have a nice collection of carbon comp resistors there and though it looks like the boards are the real problem here was an interesting commentary on reconditioning the carbon resistors from Hi Fi Collective:

Being made of organic material, they do have the tendency to absorb water from the atmosphere. This absorption can increase the actual resistance of the component, hence the slightly higher-than-normal tolerance published on this page. To fix this, remove the water from the component and seal it. The best method is to place the resistor/s on a baking tray, set your oven to 80 degrees centigrade and leave it in the oven for 8 hours. The secret is to remove the moisture slowly. If you rush, it will become noisy in the circuit. Once cooked, seal the body of the component in Shellack (preferably the flakes) to stop further water absorption. At the end of this procedure, you will have much lower noise and more closely tolerant resistors.

https://www.hificollective.co.uk/compon ... stors.html

Honestly, if this were mine I wouldn't bother with reconditioning the boards - a lot less hassle and peace of mind to just make new ones - but here were a couple of fun videos that seem up your street




There are a couple more videos after these...

The values of the carbon comp resistor is pretty good. The problem is definitely with the board. I’m getting 20VDC to 30VDC on empty sockets. If these eyelets had small value resistors on them the voltage on the eyelet would be insignificant, but they don’t.

[Stephen1966]

The damn things need to be tested with a megger...

I had a look around and these are a good price if you're going to be needing them regularly

KIYORITSU
ANALOG INSULATION / CONTINUITY TESTER
MODEL 3132A

https://www.kew-ltd.co.jp/en/products/detail/00973/