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Tube damaged - how sensitiv are they?
Old 3rd January 2011
Gear Nut
Misaria's Avatar

Tube damaged - how sensitiv are they?

I just got a 12AX7 tube I ordered, amongst other things. Unfortunatly they didn't pack it very well and I'd say about 3 pins on it are bent..
Should I try unbending them and using them in my preamp? Or can it damage the preamp if it doesn't work / it's broken?
Old 3rd January 2011
Lives for gear
If the pins are just bent you can go ahead and straighten 'em up,
as long as they don't break you'll be fine, and no it won't damage the pre even if let's say the tube got other damages (es the filament inside etc..)
Just make sure you don't damage the glass, if air gets in you will waste the tube

Lotsa NOS tubes have the pins slightly bent, no problem when you put them back in place
Old 3rd January 2011
Gear Nut
Misaria's Avatar

Thanks for the quick reply!
Good to know, hope no air has entered the tube..
I'll carefully straighten them and hopefully the tube will work!
Old 3rd January 2011
Lives for gear
fireberd's Avatar
When I was working as an amp tech, back in the early 70's, I had a "pin straightener" that I kept in my toolbox to use in situations such as this.
Old 3rd January 2011
Lives for gear

The thing is that you mustn't stress the point where the pins enter the glass.
One suggestion has been to use an old 'biro' pen with the middle pulled out to gently straighten the pin.
Whatever you do to the valve it is VERY UNLIKELY to damage the gear itself as a valve is essentially 'open circuit' until the heater has got things warmed up, so no current flows until hot.
If air did leak in, it obviously won't work as a valve and the heater will glow a bit brighter and burn out quite quickly as the heater wire will react with the oxygen in the air, a situation that is prevented by it being a vacuum normally, the same as lightbulbs.
If air does leak in the inside of the glass usually turns 'milky' white.
Matt S
Old 3rd January 2011
Gear Nut
Misaria's Avatar

Thanks for the advice guys!
I used a "Phillips screwdriver" (? It's the translation I got).
The space between the edges kept the pin steady.. although the pen-trick was a good idea, hopefully I'll never have to try it.. :D

The tube works!
Old 3rd January 2011
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