Flashover damage

[Sowhat]

I have a Mesa Engineering dual rectifier solo head 100 in for repair that has suffered a pin 2 to 3 flashover on one of it's output tube sockets. The sockets are ceramic in these things and the flashover damage vaporized the glaze coating on the ceramic but not real deep. I have been able to scrape off the scorch mark revealing white raw ceramic. My question is if the socket is still viable. I know that plastic/bakelite/micalex sockets are pretty much toast if this happens to them because of the carbon residue the vaporized organic socket material produces but ceramic sockets have no organic compounds, they are just essentially glass, right? There's no crack or tunnel (at least none that I can see) and the only thing that's missing is the fired glaze coating on the ceramic between these two pins. It's a big pain to replace octal sockets in these amps because they are buried so deep under the boards and chassis and wiring, if you think I can safely avoid this or you know of some repair magic, you would make my day.

[soundguruman]

I have a Mesa Engineering dual rectifier solo head 100 in for repair that has suffered a pin 2 to 3 flashover on one of it's output tube sockets. The sockets are ceramic in these things and the flashover damage vaporized the glaze coating on the ceramic but not real deep. I have been able to scrape off the scorch mark revealing white raw ceramic. My question is if the socket is still viable. I know that plastic/bakelite/micalex sockets are pretty much toast if this happens to them because of the carbon residue the vaporized organic socket material produces but ceramic sockets have no organic compounds, they are just essentially glass, right? There's no crack or tunnel (at least none that I can see) and the only thing that's missing is the fired glaze coating on the ceramic between these two pins. It's a big pain to replace octal sockets in these amps because they are buried so deep under the boards and chassis and wiring, if you think I can safely avoid this or you know of some repair magic, you would make my day.

The flash over is caused by a bad tube, wrong impedance speaker or defective speaker, bad speaker cable...
Most of the time, wrong speaker impedance....using a shielded guitar cord as a speaker cable.
You have to identify those causes and correct them, or it will happen again.

Once the arcing occurs, the socket is junk. You cannot scrape the carbon off, it will just start burning again.

Do not assume that your speaker or speaker cable is good, even if it's new.

As much as you wish that the socket is OK, it's not. It must be replaced.

Yes, Mesa amps are a huge pain in the rear to repair. Very time consuming, and expensive.
Requires professional soldering equipment. Do not attempt to repair it yourself, have a professional do it.
The circuit board is very easily damaged by inexperienced persons.

There is no "repair magic." Don't believe it. There is no "spray on" cleaner that cures arcing.

If you do not identify the cause, such as wrong impedance speaker, bad speaker cable...
IT WILL happen again, and continue to burn.

MOST musicians IGNORE speaker impedance. This is what gets you into all kinds of problems.
Incorrect impedance will damage tubes, tube sockets, or wreck your output transformer. BELIEVE IT!

This is WHY, on every amp I repair, the speaker, and speaker cables are carefully tested and checked.
Quite often, I find defect speaker cables. Even new ones are defective.
Defect speaker cables cause many, many expensive breakdowns. Incorrect impedance causes many, many problems.

If you thought that you could plug any amp, into any speaker, with any cable, you are VERY wrong.
Get a GOOD tech to check everything, and get you on the road to reliability.

If you would like me to check it, or repair it, fine.
You will have to drive 4-5 hours, both ways, San Luis Obispo, central Coast.

But there are lots of good techs in OC. Hire whoever you please.

[Sowhat]

Quite the dissertation there soundguruman,

The chain of events that led to the flashover are quite unique and interesting in itself. That has been remedied. I have come across this type of failure countless times over the last 50 years but the question was about the nature of ceramic insulating material, not the pitfalls of flashover. I've dealt with this type of failure more times than you could shake a stick at.

Still... posting that reply as you have is good to have in this forum for others who may not be highly experienced Electronics Engineers with comprehensive state of the art equipment and facilities. I post these questions more food for thought rather than a plea for help. Maybe I just don't make myself clear sometimes. :-)

[soundguruman]

Yes you are trying to avoid changing a tube socket.
No go.

[Jazz P Bass]

If all of the the carbon flashing was removed, what's the big deal in letting the socket in.

I repeat, "If all of the carbon flashing was removed".

You said the glazing is gone.
The underlying material may be porous, though.
That may be a problem with humidity.

How about a picture?

[soundguruman]

The heat from flashover eventually turns the ceramic TO glass.
So, it's not really glass to start with...but after baking at 2000 degrees for a bit...you get glass forming in the burn zone.

Scraping the carbon off is wishful thinking....there is still micro carbon threads in the ceramic...

Flash is almost always result of wrong impedance.
But, could have spilled a beer in there...

And I say that because,
Fixing amp is one thing,
Preventing future repeat failure is the other HALF of the repair job.

[Sowhat]

Just though I would give it a try and load tested the amp a full undistorted output. I't made it nearly an hour when ZAP!!! another flashover. You're right, you just can trust a socket that has flashed no matter what it's made out of. And that was at a properly loaded output.



It's a shame because it looked so clean and hopeful under the magnifier before I did this test but I guess you can't see everything. I wonder where the carbon came from... upon real close examination I don't think it's carbon... looks a little like sputtered metal, maybe vaproized from the pin sockets?
Anyway, it's out with the old and in with the new.

[g1]

Assume this second flash over was with a different tube in there? You may want to do the same extensive test with the new socket.

[Sowhat]

It's getting new tubes anyway and some other stuff here and there that the customer broke like that pot in the background. The amp leads a tough touring life and has got it's share of bangs and bruises like the destroyed 16 ohm output jack that started this whole ball rolling. For some perspective he uses a 16 ohm cabinet but when he wrecked the 16 ohm jack he plugged into the 8 ohm jack. Mesa kind of stupidly states in their manual that the amp is pretty tolerant of impedance mismatches which is why the customer figured that was O.K. and under normal circumstances it very well might be only being a 2:1 mismatch. But this is where the story gets interesting. Putting a higher than expected impedance speaker on the output transformer still makes it prone to developing flyback currents under the right conditions. At the venue they were playing power cutout 4 times on the band with the resulting 4 power surges when power was restored. The band did not bother to shut down their amps during the blackouts so it was full surge each time. After the 4th blackout the Mesa began to behave badly and this is how it came to my shop. Hammer something long and hard enough and it will break. Maybe they can get some compensation from the venue for this repair. An interesting sidenote to this is that the venue manager rather than bringing in another circuit for the bands power needs, he just kept hitting the breaker. At one point in this maylay he unplugged the stage fans to try an mitigate the power draw situation, and midday in Vegas gets pretty hot... the band nearly slit his throat for that stunt.

[soundguruman]

Just though I would give it a try and load tested the amp a full undistorted output. I't made it nearly an hour when ZAP!!! another flashover. You're right, you just can trust a socket that has flashed no matter what it's made out of. And that was at a properly loaded output.

[ATTACH=CONFIG]27318[/ATTACH]

It's a shame because it looked so clean and hopeful under the magnifier before I did this test but I guess you can't see everything. I wonder where the carbon came from... upon real close examination I don't think it's carbon... looks a little like sputtered metal, maybe vaproized from the pin sockets?
Anyway, it's out with the old and in with the new.

You are learning the Jedi repair ways of the FORCE.
No, there is no way around it.
Once the flash occurs, there is carbon embedded in the socket...and it will continue to burn.
So, order some sockets...take it to a tech with great soldering skills.
I can do this in about 1 hour or less. I check the speakers for free.

Remember- make sure your speaker / speaker cable is 100% - or suffer the repeat failure.
Change your output tube, it's dusted.

[Sowhat]

I can do this in about 1 hour or less. I check the speakers for free.

Yeah, so can I. I don't need to order them, got em in stock. You keep soliciting for your services here, are you low on work? I got this covered old buddy, thanks anyway.

[soundguruman]

No, I just encourage people to use professional for Boogie amp.

Due to soldering, which is challenging, because of plated thru holes, which are easily damaged.

And because you are in driving distance to my shop.

No, there is actually a waiting list of customer appointments...

[tedmich]

there is some evidence that ceramic insulators, for all their prettiness, perform less well than non-ceramics when it comes to contamination and flashover, at least in the kV systems that are studied a lot.
IEEE Xplore Abstract - Flashover mechanism of non-ceramic insulators
of course Bakelite isn't as good an insulator as silicone rubber, Micalex is pretty good, and PTFE is only $20
http://www.thetubestore.com/core/med...6c1d1148c5f282
$70 if you go with the tellurium copper pins...

[Jazz P Bass]

Eewww!

Heater to plate.

[Justin Thomas]

Looking at those 3 sockets, maybe it's just the perspective, but it seems there's less actual ceramic material between pins 2/3 of the charred socket. On the one on the right, 5/6 seems the same. Does it look even on your end, or is it just my perspective? I wonder if the tube lit up like my friend's 6L6GC when he didn't realize the guide pin was snapped off that one time...

Justin