Tracing noise problem, TwinRev.

[nosaj]

Will do 1st thing AM pdf. So just lug to lug missing out the wiper..old

Thinking more on the dreaded conductive board scenario (which would be a huge disaster/ Im hoping massively it's a component failure instead)..

When I prized the baffle off the velcro, just tarting bits up etc, I was surprised to find lightgreen dry ( seems to be) mould: a thin uniform film had got in this gap, IE the 3mm gap due to the velcro patches separating the two chipboard surfaces.

So with the two main boards sandwiched together, the lower one to prevent components on theunderside shorting to the chassis.. I wonder if green mould might have similarly got in here. Similar tiny gap. Mould tends to thrive on wall in gaps behind cupboards, behind furniture very common here etc.

Its only a theory to consider if, hopefully not, I don't find the cause. Heck of a job to unsolder loads to lift it up to see. Last Resort Idea !!

Thanks, SC

Mold needs moisture.....so there ya go.
nosaj

[Sea Chief]

Mold needs moisture.....so there ya go.
nosaj

Of course, but I can't help thinking that the conductive board possibility is being suggested because I mentioned this prognosis which was made on this amp as it was ( effectively/ in essence ) prior to me buying it, in a city far away from here.

When Ipicked it up, I knew it was blown. I bought it as blown. I saw awful mods done on it, all different power tubes one frosted. It wasn't turned on here. So it was posted to Rift again hundreds of miles away. Many many tests done there... before he concluded it must be a conductive board.

He was right, because once Id rebuilt it with a new board, it sounded fine.

At this point the amp's main board bears no resemblence with regard to the original binned circuit board before. There is no correlation between the local conditions that caused the original board to become conductive over 41 years, to here/ this totally different & new board now.

Im not sure if this history is being understood you see. I can't explain it any clearer, but as I tried explaining my simple 8/16 amp question without it being understood, the chances of what Im saying here is very likely not to be understood either.

Is the history Ive just outlined easy to understand? Or, is it a convoluted mess of picture, my point unknown?

Thanks, SC

[Dave H]

Now then, am I only needing to test it without rotating the knob? The noise is so loud & unsettling even touching the damn vol knob, so if this test is needed at various points on the rotation.. Im stuffed/ it's too scary a prospect, unless that is I briefly unplug the speakers.

You've changed V1 a few times and measured for DCV on the vol pot, the next thing I'd do is to change the pot just to eliminate it before I'd consider changing the board.

[pdf64]

Yes, if not a bad valve or DC leaking somehow (70mV should be fairly insignificant), then a crackly vol pot is probably either just a bad pot, or oscillation, and ghe latter seems unlikely.

[Chuck H]

Of course, but I can't help thinking that the conductive board possibility is being suggested because I mentioned this prognosis which was made on this amp as it was ( effectively/ in essence ) prior to me buying it, in a city far away from here.

When Ipicked it up, I knew it was blown. I bought it as blown. I saw awful mods done on it, all different power tubes one frosted. It wasn't turned on here. So it was posted to Rift again hundreds of miles away. Many many tests done there... before he concluded it must be a conductive board.

He was right, because once Id rebuilt it with a new board, it sounded fine.

At this point the amp's main board bears no resemblence with regard to the original binned circuit board before. There is no correlation between the local conditions that caused the original board to become conductive over 41 years, to here/ this totally different & new board now.

Im not sure if this history is being understood you see. I can't explain it any clearer, but as I tried explaining my simple 8/16 amp question without it being understood, the chances of what Im saying here is very likely not to be understood either.

Is the history Ive just outlined easy to understand? Or, is it a convoluted mess of picture, my point unknown?

Thanks, SC

You refuse the possibility that the board is conductive, why? Is it because that prospect is too horrifying so you refuse to even acknowledge it? You can't reconfigure facts. They simply are.

We understand that the board is new-ish. We understand it was provided as new for that purpose and you believe it should therefor posses relative wonderfullness for the purpose. We understand the amp is no longer in the circumstances believed to have caused the original problem. None of this is diagnostic though.

The amp STILL has mold growing on the speaker. Likely feeding on organic material used for the adhesive. Mold requires food and considerable MOISTURE. Without sufficient moisture there is no mold. It would be old, dry, dead mold.

Regardless of age or relative newness the type of board in the amp NOW can absorb moisture. Which is apparently present BECAUSE THERE'S MOLD GROWING ON THE AMP.

But go ahead and keep your horse blinders on if you're enjoying that. We'll talk about the amp again in another year when you decide to revisit the project because the amp still isn't fixed.


Just blow dry the damn thing. It's already open.

[Sea Chief]

You refuse the possibility that the board is conductive, why? Is it because that prospect is too horrifying so you refuse to even acknowledge it? You can't reconfigure facts. They simply are.

We understand that the board is new-ish. We understand it was provided as new for that purpose and you believe it should therefor posses relative wonderfullness for the purpose. We understand the amp is no longer in the circumstances believed to have caused the original problem. None of this is diagnostic though.

The amp STILL has mold growing on the speaker. Likely feeding on organic material used for the adhesive. Mold requires food and considerable MOISTURE. Without sufficient moisture there is no mold. It would be old, dry, dead mold.

Regardless of age or relative newness the type of board in the amp NOW can absorb moisture. Which is apparently present BECAUSE THERE'S MOLD GROWING ON THE AMP.

But go ahead and keep your horse blinders on if you're enjoying that. We'll talk about the amp again in another year when you decide to revisit the project because the amp still isn't fixed.


Just blow dry the damn thing. It's already open.

Chuck I am not refusing to believe the board is conductive, but arguing for the unliklihood considering how new it is, hiw stiff the board is. It is rock solid, so I just can't physically envisage how moisture can have got inside it in so little time without the structure showing some signs of ingress, some signs of moisture having affected it; it looks brand new still.. totally unlike the waxy flexible papery definitively conductive thing I removed from 41 years inside it.

The mould I find, you will likely imagine as a dampness. Not so: is light green, a chalky dry film. Now Im not discounting that a similar dry film might be underneath the board on it's underside, no, Im simply just saying no physical dampness is found in the amp, just dry dusty like --indicators-- of the enviroment having some damp. This is different.

Having once done a redo of a conductive board, I know what a massive undertaking job it is. It has to be the most comprehensive, apart fom building a whole amp from scratch. Therefore, before I come to this conclusion, I must logically rule out every prior possibility. Which is exactly what a professional amp maker did, comprehensibly with some time with this very amp, before. I don't know what he did. I am really just trying to explore a similar path. Testing xyz component. Perhaps replacing one as an 'educated try', other ideas.... until.... I come to the conductive board hypoethesis.

The fact that only on page 1 it seems, a few seem absolutely certain the problem is a conductive board, seems very oddly & hugely premature to me. That's all Im saying too/ my other point being.

Fwiw I pummelled it with a fan heater today for well over an hour, so thoughrally going L to R in steps to not miss a bit, the chassis was almost too hot to touch. Reput tubes back. Turned amp on, gtr plugged in, with ear defenders on, & such a huge POP almost the worst yet.. scaring the daylights out of me/ noise resolutely there still.

I will bet money now, that it is a bad component. That's just my feeling. I know this might seem nuts. But exploring the possibility of this avenue.. I know from what Rift did, is not; furthermore it seems the logical & correct approach at this stage too.

Thanks for your ideas/ help. SC

[Helmholtz]

Too much talk, too little results.

If the hairdryer treatment improves things, the problem is moisture.in the board.

Some with pot: replace or clean and you'll see.

[nosaj]

Maybe you would be best served by taking the amp to a shop.
nosaj

[Chuck H]

Well with the info that the mold IS indeed dried up and possibly an artifact, a fan/heater blowing into the amp for an hour, "too hot to touch" and still no change I'll let the probability of a conductive board go for the moment.

Thank you for entertaining the notion and attempting to dry it out. My current hypothesis then would be a bad solder joint or joints. They don't always manifest when made but can present themselves at any later date. My own soldering skills are less than professional and I've had this problem on a build before that didn't show itself for over a year. Thankfully this wasn't on an amp I built for someone else. But then, I tend to work more cavalier like a mad scientist when modding my own stuff and I am more fastidious with customer builds.

Maybe try g1's suggestion and put V2 back in, but stay plugged into the normal channel. Did the expected gain return?

[Randall]

Maybe I don't know much about much, but I do know this. FIBERBOARD SUCKS. I say this as I am currently in the second time to rebuild a Fender Bassman that had a bad original black fiberboard, that I rebuilt on grey fiberboard. It went conductive, contrary to opinions that it does not. And right now I am building it again at my own time and cost on garolite. Add to that a traumatic experience with a Fender Deluxe Reverb build that had a bad new black fiberboard from MojoTone right from the beginning. I had to tear that out and re-do it also.

I WILL NEVER AGAIN use fiberboard for anything, even to wipe my A$$.

[pdf64]

The biggest problem with fibreboard is that most of the time it doesn’t cause problems, so people carry on using it. But when it does play up, it’s a complete pain in the arse to resolve it.
There seems to be a complete ‘turning a blind eye’ about its unsuitability by the kit / DIY supply industry, which seems very disingenuous to me. It would even be fine to sell the customer a vintage correct turd if that’s what they want, provided the supplier gave full disclosure.
But I’m mystified why some boutique builders (eg Rift) continue to use it, when they must have encountered occasional issues caused by it.
Here’s a rather severe case that came to mind, reported over on TGP a while ago https://www.thegearpage.net/board/in.../post-26339181

[Chuck H]

Regarding the black fiber boards...

It's not only moisture that can cause conductivity. I have only seen this on the older ones. Twice in silver face Fenders and once in a Traynor. The boards, which weren't conductive initially did become conductive after extensive reworking and modification. It was a small amount of conductivity, but causing enough trouble to keep me from putting my stamp on the projects. Both the Fender boards were heavily waxed, as was typical with some silver face amps I have to think. I expect the wax introduced by Fender at some point was intended to mitigate the absorption of moisture. Something to consider. It's apparent that Fender was well aware of the conductive board problem in the 60's. Anyway... I think that the application of heat from extensive resoldering and/or flux core type solder residue (which cannot be effectively cleaned from black fiber boards) combined with the actual carbon in the board material somehow aligned or conditioned all said elements into semi conductive pathways on/in the board that could not be eliminated by drying. and to this I can only say...

What knucklehead somewhere in history thought that soaking a circuit board, intended to be an insulator, in the same element used to make the semiconductors to be used on said board was a good idea!?! As if having the board be black in color were more important than it's actual function. And on that note...

It's even stupider (or shiftier) that some outfits perpetuate this long known problem and sell this unsuitable product to unwitting customers.

[Sea Chief]

Regarding the black fiber boards...

It's not only moisture that can cause conductivity. I have only seen this on the older ones. Twice in silver face Fenders and once in a Traynor. The boards, which weren't conductive initially did become conductive after extensive reworking and modification. It was a small amount of conductivity, but causing enough trouble to keep me from putting my stamp on the projects. Both the Fender boards were heavily waxed, as was typical with some silver face amps I have to think. I expect the wax introduced by Fender at some point was intended to mitigate the absorption of moisture. Something to consider. It's apparent that Fender was well aware of the conductive board problem in the 60's. Anyway... I think that the application of heat from extensive resoldering and/or flux core type solder residue (which cannot be effectively cleaned from black fiber boards) combined with the actual carbon in the board material somehow aligned or conditioned all said elements into semi conductive pathways on/in the board that could not be eliminated by drying. and to this I can only say...

What knucklehead somewhere in history thought that soaking a circuit board, intended to be an insulator, in the same element used to make the semiconductors to be used on said board was a good idea!?! As if having the board be black in color were more important than it's actual function. And on that note...

It's even stupider (or shiftier) that some outfits perpetuate this long known problem and sell this unsuitable product to unwitting customers.

Ok thanks for taking my points on board (pun sadly intended). Im not ruling out the conductive board idea, even having done the dryer without results. But discussions on board composition & opinions on favourites or whatever, I'm not sure helps me out at this juncture.

So if I could please just do all I can putting this board theory -last- & carrying on normal tests beforehand. I would really appreciate help on this avenue.

I simply have no other option at this stage, as pulling the whole this apart & rebuilding it again, or more likely just selling it as it is as 'dead', is hugely massively uncalled for & premature it seems to me at.

---

Can I just go back a step. I need to explore possibilities of a bad component, first port of call. Then I can explore a possible bad solder joint. Ok. Now these two avenues, so far as I know, can be helped by pulling tubes to " isolate " / " narrow down " the areas helping matters at least. This is what I need help on.

Ok pdf has suggested try replacing the Normal vol pot, & I read on a similar schematic ( ul 135 n/a ) its likely a 1m-A.

But before I try this, is it not the case that if pulling V1 & the noise still being there.... is that not proof that Normal vol pot is ruled out as culprit?

I just need to go in tiny steps, with the notion ( whether or not is is ultimately the correct theory for now ) that it is either a bad component -or- solder joint, by a process of elimination. I think too, that this is a perfectly normal course of action with a faulty amp.

Thanks, SC

[nosaj]

Start with solder joints first. Just reflow every single one of them, then look at components.
nosaj

[Sea Chief]

Start with solder joints first. Just reflow every single one of them, then look at components.
nosaj

Understand this. But Ive never had one bad solder joint, ever (& often get the impression that because its known my amp knowledge is limited, that my joints are likely sub par). And isn't it just as likely, if I were to just blanket-redo them all, that I'd make one bad solder joint anyway?

I would prefer to look at components first tbh; not only bc it is a far smaller prospect in terms of workload/ it does seem logical to go for the easiest avenue first, whatever it might be to attempt fixing... no?

Furthermore if the amp worked great before, doesn't that suggest the solder joints are indeed fine? IE how would a solder joint degrade, in such a relatively short time? This avenue therefore just from logical pov, doesn't seem -that- plausible. Like the possible conductive board, Im not discounting it though.

If I could just concentrate on the component tests, before more complicated avenues, that would be great.

Thanks SC