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Can really dirty power cause power tubes to arc?
http://maplifiers.net/forum/viewtopic.php?f=7&t=1424		 Page 1 of 1
Author:  knope [ Wed Mar 16, 2011 10:47 pm ]
Post subject:  Can really dirty power cause power tubes to arc?
So a few days ago the power tubes in my amp started arcing. At first I thought it was my amp, but I just was checked the Carvin from the same outlet and the completely different set of power tubes that where in the Carvin started arcing too.

Could really dirty power from the outlet cause this? They both look normal until i flip the standby.
Author:  chris_d [ Wed Mar 16, 2011 10:52 pm ]
Post subject:  Re: Can really dirty power cause power tubes to arc?
Arcing power tubes are bad news. Are you sure they are arcing, and not just doing the gas flashing blue-ish thing?

I suppose you could be getting surges on that outlet.

Also make sure that you are using good speaker cables, not shielded instrument cables, and that the plugs on them are in good shape and soldered well.

Lastly, what are the rectifiers in both amps?
Author:  knope [ Wed Mar 16, 2011 11:23 pm ]
Post subject:  Re: Can really dirty power cause power tubes to arc?
chris_d wrote:
Arcing power tubes are bad news. Are you sure they are arcing, and not just doing the gas flashing blue-ish thing?

I suppose you could be getting surges on that outlet.

Also make sure that you are using good speaker cables, not shielded instrument cables, and that the plugs on them are in good shape and soldered well.

Lastly, what are the rectifiers in both amps?


Definitely arcing, they weren't doing that before and the tubes aren't new enough to have leftover gas. Its not instant death flash arcing though...

I just checked the cable and it just might be the problem... the cab reads a resistance of 6.8 directly from the speakers, but when i check the resistance though the speaker cable it jumps to 8.0. :mob:

Carvin is SS only... it happens on my build on both tube (5AR4) and SS rec
Author:  chris_d [ Thu Mar 17, 2011 11:38 am ]
Post subject:  Re: Can really dirty power cause power tubes to arc?
Don't use that cord anymore then. Buy or build, a new good cord. If your speaker cable is wrong, you can straight up kill your power tubes, AND your OT.

Just to state the obvious, a speaker cable should just be two conductors, both unshielded, like the same stuff that is used for cords for lamps. Never ever use instrument cable for connecting speakers. You probably already know this, but i am just saying it here anyhow.
Author:  knope [ Thu Mar 17, 2011 1:01 pm ]
Post subject:  Re: Can really dirty power cause power tubes to arc?
Bah! When I left my band I accidentally left my spare speaker cable and two instrument cables. And whats worse is that I only have one spare 1/4" plug :mad:

Anything I should check to make sure my amp is ok? Stupid cable... I bought it 14awg just to be extra sure something like this wouldn't happen :mad:
Author:  chris_d [ Thu Mar 17, 2011 1:08 pm ]
Post subject:  Re: Can really dirty power cause power tubes to arc?
You are going to want to look inside both amps at least. If you see any black markings on or around the tube sockets, you need to replace the sockets, and the resistors attached to them. Then you are probably going to want to avoid using those tubes, depending on how bad they arced.

If you are lucky, you noticed it early enough and you only suffered some slight flashing. But a severe short in the output section can take out resistors, sockets, tubes, and OTs.

But yeah, at the very least, open up both amps and look over them very closely for ANY signs that something in there sparked or shows any signs of discoloration and carbon/burnt anything.
Author:  torgeot [ Thu Mar 17, 2011 2:10 pm ]
Post subject:  Re: Can really dirty power cause power tubes to arc?
chris_d wrote:
Just to state the obvious, a speaker cable should just be two conductors, both unshielded, like the same stuff that is used for cords for lamps. Never ever use instrument cable for connecting speakers. You probably already know this, but i am just saying it here anyhow.

This is something that needs to be brought up to people frequently. When I was a pup I found out the hard way.

I recently went to a rehearsal studio and they had shielded cable between the map/speeker. I bring my Rebel 20 because I hate their map. I also always bring my own speaker cables, as I've wired them and I know what is in them.
Author:  metalfanat1c [ Thu Mar 17, 2011 2:17 pm ]
Post subject:  Re: Can really dirty power cause power tubes to arc?
My speaker cable used to be a 50 foot extension cord. One of the super old school 12awg 2 conductor ones. It's orange, and it's indestructible. My soldering job isn't... but I digress. :rawk:
Author:  knope [ Thu Mar 17, 2011 11:46 pm ]
Post subject:  Re: Can really dirty power cause power tubes to arc?
Nothing visibly burnt and everything seems fine. The arcing was on the inside of the tube pretty much a blue current going through the inside of the structures of the tubes. Kinda what I would expect if there was just a little too much voltage or current going through the tubes. No flash nor nothing serious I guess... just some "light" arcing if that makes sense. :idk:

I have to check around the house to see if there is anything I can hobo into my new speaker cable. :idk:
Author:  Zozobra [ Fri Mar 18, 2011 6:50 am ]
Post subject:  Re: Can really dirty power cause power tubes to arc?
I had a mullard fail in my speedtwin years ago and that arc'd internally but I put it down to the screens having enough of the punishment and shorting (500V plates and screens, 1750R primary!). Couldn't find any traces on the sockets and the screen resistor was fine too. But yeah, check it over and make sure.
Author:  knope [ Sat Mar 19, 2011 11:44 am ]
Post subject:  Re: Can really dirty power cause power tubes to arc?
Can I get a check list of everything I should check? Its not the cab,cab's jacks, nor speaker cable as I cleaned up all the connections and everything is now giving me the normal reading of 6.8 ohms, but the power tubes are still arcing. Not my pic but it looks kinda like this with the blue glow inside of the tube structure.

Image
Author:  chris_d [ Sat Mar 19, 2011 11:57 am ]
Post subject:  Re: Can really dirty power cause power tubes to arc?
A blue glow is usually just normal fluorescence. If it is the blue stuff only, your tubes might be normal.

If it is a sharp spark/flash, that is generally more what arcing is. The one amp i had that had shorting power tube sockets used to do a thin bright white light/spark, that was accompannied by a distinct fizzle sound with a following slight cutout. I noticed but ignored it, until the one time that the slight cutout, became permanent. :red:
Author:  chris_d [ Sat Mar 19, 2011 12:00 pm ]
Post subject:  Re: Can really dirty power cause power tubes to arc?
Oh hey, a quick google just now, renders this result with explanations: http://www.netads.com/~meo/Guitar/Tubes/blue_glow.html
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