6L6 with a hole in it....picture enclosed

[Garydean]

It's hard to tell from this picture but there is a hole in the top of this 6L6.


What may have caused this? The other tube is visually fine. The amp is a Fender Blues Deville Re-issue. The amp is only a few years old, original tubes. Can I just pop in a new set of 6L6 tubes or should I check the bias?

Thanks for the advice!!

[Alex R]

It got very hot and the glass melted. Could have been a short in the tube or a bias supply failure of some sort. First thing is to make sure you've got a bias supply. Ask if you need to know how to do this.

[Garydean]

Thanks Alex,

I should have appropriate voltage readings on the grid and screen?

[Alex R]

Yes, check pins 3, 4 and 5 (from above, count ccw from the lug in the centre). 3 and 4 should have similar high voltages and the same from socket to socket. Pin 5 should have a negative bias voltage around -50v.

[TD_Madden]

Interesting pic; I've never seen a hole in that location, only in the side.

[Chuck H]

Maybe you can patch it with duct tape

It reminds me of something I read in the Weber book about an amp that was sent to him for repair with a note that read: "This amp is shot." Someone had literally shot the amp with a 38.

If you do find that the amp does have bias voltage you may still want to open it up and inspect the tube socket for char, damage or loose componants before plugging in new tubes.

Chuck

[TigerG]

Speaking of shot...

a friend of mine once found a vintage Blackface Deluxe Reverb out in the boonies that someone had been using for target practice. It had a couple bullet dents on the face, some bullet holes through the top, and a bullet still inside the chassis, but the only thing that kept it from working was that one of the wires to the speaker jack had been shot off.

[Chuck H]

I wouldn't even restore that amp cosmetically. Bullet dents and holes in your BF...Cool. Great conversation piece. I'd have to make up some kind of story about how it saved my life when I used it for a shield in a gunfight or something

Chuck

[Garydean]

I did check the bias and it was exactly -50. I'm wondering now if the guy didn't hit the tube while extracting all the foot pedals he has stored in the cabinet.

[Alex R]

Is it a sharp-edged hole? Or a sort of melted-in hole? Bit hard to see.

[Garydean]

ah...good question. It's a sharp edge and from the looks of it, something hard poked it. No glass on the inside.

[Alex R]

Ah, forget the melting thing then, it just took a knock. Tubes do sometimes melt holes in the glass, they tend to have rounded-in edges like a sort of vortex shape, and it looked a bit like that in the pic.

[Enzo]

Actually, the melters look cool. The glass softens till it starts to melt, then the vacuum pulls it inwards. You get this rounded edge pit. Especially on horizontal mounted power tubes.

[Mars Amp Repair]

Agreed,
I also noticed from the pic, that the red painted label on the tube would have been darkened had the tube gotten hot enough to 'melt' a hole...as you have observed, the hotest part of the tube is on the side where the plate is.

We used to see the glass melted & sucked in as Enzo is referring to quite often on the old color tube tv's...this occurred when the horizontal oscillator quit & there-by removed the bias from the horiz output tube...it was really just a power tube designed to function at or around 15kHZ scan rate...blah blah blah ramblings of an old tech!....glen