5150 hideous death

[tedmich]

working on my 5150 again, found this modded board pic online



LOL!!

[Enzo]

Ewg...

[Chuck H]

I can understand not wanting to remove the board, but that's crap. OTOH, wouldn't the board have needed to come out to remove the old caps? You might be able to solder the wired from on top, but not well. Maybe whoever did that just RIPPED the old caps out to access the holes or maybe the component leads were still there?

I'll admit that on Mesa boards with the rebranded ATOM caps (axial) I have snipped out the old caps, leaving the leads sticking out of the board and then loop/bend soldered them to replacement caps. Seemed like a perfectly acceptable connection and way easier than removing the board. But I would never even think to try something like that with radial caps.

[The Dude]

Hard to tell for sure from the picture, but I suspect that the repair was done as it was because the replacement caps were too tall to solder in as the original caps were and fit into the cabinet. It's still not acceptable. That's what rulers and calipers are for. It might have been a good idea to measure the original caps and replace them with something that would fit into the amp.

[Gingertube]

2) Creepage, which is current travel along the surface of an insulator due to humidity and contamination. This IS the big issue with leakage and arc through. The number depends on the material, humidity, flux and all sort of contaminants. I have to get the book to know the general number. This is spec in CE test manual. I personally do not believe the fiber material have conductive issue, more because of the flux on the surface, the moisture it attracted on the surface that cause the problem. I can tell, Fender do not clean out the flux on the fiber boards, if people start monkeying with mods, they add more flux on the surface every time they solder stuff on. I think that's what's happening. Scrape the flux off the surface when the flux solidified and see whether you can fix the leakage.
.[/B]

I do airborne electronics PCB's for a Laser Airborne Depth Sounder survey system - 2 examples: Q-Switch Driver boards for the laser at 4.5kV and Photomultiplier Power Supply (for the Laser Receiver) at 2.5kV.

FR4 boards are fine - get the layout right, clean bare boards thouroughly before loading, again after loading and then finally spray with Conformal Coating. The last step (conformal coating) is paramount for reliability. I would suggest that this should be standard practice for tube amp boards.

Cheers,
Ian

[Chuck H]

I do airborne electronics PCB's for a Laser Airborne Depth Sounder survey system - 2 examples: Q-Switch Driver boards for the laser at 4.5kV and Photomultiplier Power Supply (for the Laser Receiver) at 2.5kV.

FR4 boards are fine - get the layout right, clean bare boards thouroughly before loading, again after loading and then finally spray with Conformal Coating. The last step (conformal coating) is paramount for reliability. I would suggest that this should be standard practice for tube amp boards.

Cheers,
Ian

Ian,
What is the purpose conformal coating? I'm not unfamiliar with it, it's just that I usually see it used as a means of controlling moisture infiltration (which shouldn't be a problem with FR4) or squelching the growth of tin whiskers with lead free solder (which isn't a problem with most small operation built tube amps). It there is another good reason? I'd be interested.

[Justin Thomas]

It might have been a good idea to measure the original caps and replace them with something that would fit into the amp.

<BEFORE> cutting out the old parts...

Justin

[Jazz P Bass]

My take on 'conformal coating'?

It's a bitch to get off if you want to rework the pcb.

conformal_coating_removal_techiques.pdf

[Chuck H]

I got through a good bit of it. What a PITA. I agree that conformal coatings have benefits. Probably an improvement for factory built amps. Especially those with a high DNR probability, as many are now. I certainly don't think conformal coatings have any place in cottage industry amps though.

[Jazz P Bass]

Conformal coating is not needed in a guitar amp.

For what purpose?

Military, marine, aerospace, welding equipment, yes.

The gunk is made to isolate the PCB from the environment.

Well, I guess it would keep beer spills off the PCB.

[raiken]

Conformal coating is not needed in a guitar amp.

For what purpose?

Military, marine, aerospace, welding equipment, yes.

The gunk is made to isolate the PCB from the environment.

Well, I guess it would keep beer spills off the PCB.

It also greatly increases the dielectric strength of traces and pins, and changes the minimum required spacing for a given voltage. It is a good idea for PC-mounted power tube sockets.

For example, according to the IPC-2221A spec, a 32mil spacing on a component lead termination with conformal coating is good for over 500V, while the same component lead termination uncoated is only good for 300V max.

[Gingertube]

Chuck H,
I was a liitle loose in my language. Specifically, I use Anti-Corona Conformal Coating on these boards. It prevents build up of grunge and moisture on the board which may lead to arcing problems but its main benefit is that it has a dielectric strength of 48kV/mm compared to the dielectric strength of air of approx. 3kV/mm. This means that for a given track separation then a coated board can have 16 times higher voltage between those tracks before arcing.
Cheers,
Ian

[Chuck H]

Yeah, those things don't occur to me in idle thought because I still build eyelet boards. Spacing isn't an issue and a new board can be expected to last the buyers lifetime without any coating. But with new lead free solders and SMD boards that sometimes have close tolerance (and these are the amps most likely to be considered DNR if they fail) a conformal coating could add some reliability with added insulator resistance and tin whisker prevention. It might be a small benefit, but how much could the stuff cost per unit? Literally a few pennies if you're Berringer or Loud.

[Enzo]

And since most of us still use one sided boards, the difference is having to run a trace around something and maybe use a jumper, rather than thread a tiny trace between socket pins on the board.

[tedmich]

Well the OP is gonna unload a few polished PV Turds, Clist LOOK OUT!



The 5150 cleaned up pretty well, the graphics are just printed as the badges are long gone...



I though this way funny

The 6505+ looks AOK considering the guy had spray painted it entirely neon green...