Popped a tube?

[fitz]

I was just playing my new to me JCM600 when I heard a pop.
Not loud, but the amp went silent.
Turned off a nearby lamp and saw that V3 was dark, so I shut off the amp and had a closer look.
Pulled the tube and a piece literally fell off the glass.

Pulled the chassis and looked over everything.
Nothing looked out of sorts - 2 board fuses tested as fine.
Put in a different tube and everything lit up.
Seems fine now, and working as expected.

Never had a tube pop apart before.
It was a practically new JJ803S with I'd guess no more than an hour on it.

Just a random tube flaw? - or does anyone think I should investigate anything else?

 

[SteelLucky]

Not uncommon. But doesn’t happen all the time either. Test, Replace, test and move on.

 

[Gunner64]

Glad you paid $25 for that.....they never did that when they were $8, I going with that amp is jinxed, sell it while its working before it burns your house down.

 

[Jethro Rocker]

I think random too. Got a crack somehere along the road.

 

[RLW59]

I

Glad you paid $25 for that.....they never did that when they were $8, I going with that amp is jinxed

I had a vintage GE 12AX7 split all the way around the base. The whole glass cylinder came off and I had to pull it out by grabbing the plates. Decades old, 5 months in my amp, and one day no sound with a cold white tube.

Glass does weird things. You can drop a tube on a concrete floor and it might not break. Or it can crack for no apparent reason.

 

[StrummerJoe]

There was probably already a fracture in the glass. That sucks, but it's a rare - thank goodness.

Bummer that happened.

 

[Gunner64]

I

I had a vintage GE 12AX7 split all the way around the base. The whole glass cylinder came off and I had to pull it out by grabbing the plates. Decades old, 5 months in my amp, and one day no sound with a cold white tube.

Glass does weird things. You can drop a tube on a concrete floor and it might not break. Or it can crack for no apparent reason.

I've had them do that too. I had a EH 6550 in one of my stereo amps Crack around the base the same way, had to pull it out by the plates. I still have it on a shelf over my work bench. Kind of a conversation piece now.

 

[Whatwhatringrang]

wow popped right off there.

I had a excellent sounding Mullard I dropped and it was a slow leak . Worked great for a little while . The getter turned white by the next day when I fired it up . Sounded awful so I took a look however but did not break quite like that.

Good thing you did not reach back while amp was on and pull it out!

 

[Dogs of Doom]

check to make sure you have no arc residue on the tube socket...

 

[paul-e-mann]

Just be glad you werent at a gig!

 

[SteelLucky]

check to make sure you have no arc residue on the tube socket...

Not a bad idea at all. Did not see any indication of it on the tube in the picture he posted.

 

[fitz]

check to make sure you have no arc residue on the tube socket...

Not a bad idea at all. Did not see any indication of it on the tube in the picture he posted.

Yes, the tube socket looks fine - no scorch marks or residue.
Didn't have it cranked or anything.
I had just drilled & tapped a little machine screw into the snapped off presence knob shaft, and was only strumming some chords to see if the pot was functioning.
I can adjust the presence with a screwdriver until the new pot arrives in a day or two.
Wound up trying some different tubes and some different presence settings.
This amp just keeps sounding better.

 

[Spanngitter]

It might have experienced a drop or lateral force when inserted into the socket leading to a small crack..or (wha I have seen on multiple amps, especially with sovtek or similar "fat" envelope tubes is that they crack all around. In most cases, this is caused by the shroud of the shielding tube being close to the glass or even touching it, causing a cold spot and therefore thermal fracture.