Arcing tube issue

[stan]

I am not in the know when it comes to things technical. I wonder if this problem is an issue that cannot be remedied. I recently was changing an old GEC KT66 for another old stock Genalex KT66. When I turned on the amp, the replacement tube started arcing (like electric bursts from the old Frankenstein lab). Fuse, of course, blew.

Question -- is the tube gone and thus to the garbage it will go? Or is some other issue at work. As a hopefully helpful diagnostic -- I put another old GEC KT66 in its place and the amp works fine.

If this is not the appropriate form for such questions, sorry and feel free to move.

Thanks in advance for any help.

[CurtissRobin]

That old tube apparently took a mechanical hit somewhere along the line. It's toast and should be used for either a decorative craft or landfill. I'm glad the amp's still OK.

KennyO

[ajcoholic]

I had a German made EL84 that just did that. Was fine one minute... then started glowing (more like strobing) purple and pink! Like a neon lamp!

It was toast...

AJC

[zaphod_phil]

If this is not the appropriate form for such questions, sorry and feel free to move.

Since you don't normally find KT66s in Marshall 18W style amps, I suspect this question is about an amp that's off-topic for 18watt.com. PPwatt.com, 45watt.com or wattkins.com would have all been more appropriate places to ask about this issue.

I put another old GEC KT66 in its place and the amp works fine.

That's what matters most - your amp is still OK.

[stan]

Thanks so much for the very helpful responses. Good Xmas ornament -- though might remind the wife that it is very costly ornament!

You are right. If goes to a very old Carr Mercury (serial #1 in fact). So, probably belonged elsewhere. Sorry, won't, screw up again (at least in this manner -- likely to screw up in other ways, unfortunately).

Thanks again, stan

[chabby]

That could have been a costly lesson as I just replaced the PT in aCarr Rambler that had an arcing 6L6. Not only that but the guy who owned it switched it from pentode to triode without hitting standby first. That along with an arcing tube took out the PT.

But I've seen just an arcing tube take out PT's too. The Carrs have some PT protection devices in them though and they can soetimes save you. The kicker is that once those mechanisms have been triggered once, they are done and no longer protect the PT. So you might want to check the two caps wired up under the power switch and over to the right near the standby switch. They are supposed to help blow the fuse before the before things get to the level that can take out the PT.

My friend's amp had apparently had an eralier event render those fail safes dead before the even that took out the PT. Carr has magnificent customer service.

[stan]

Thanks so much for the "heads-up". Oddly, what happened (and it happened twice since I tried the old arching tube twice -- with the same bad effects! -- talk about stupid!!), is that the fuse blew both times. Charmed amp?

Anyway, disposed of expensive, yet potentially more expensive, Genalex Gold Lion, installed another NOS of same model and the amp (sorry, I know this is about 18 watters -- but the good advice I have received could save someone some serious damage with their 18 watter [heck, glad I didn't have this issue when changing the Mullards in my 1965 18 2X12]) and things now work very well. I play around 2 hours per night with the Mercury (since it is so quiet it does not wake anyone in the house) and hope to get about a good 3-5 years out of the power tube.