Faulty 12AU7 tube?

[Jimb0]

Hello,

I believe I may have received a faulty 12AU7 tube. I’m getting a high reading on OB and a low reading on OA. With all my other tubes, the voltages read normal, and I’ve also tried this tube in two different Crack amps with the same result.

With the faulty tube I get these readings:
OB reads 142v
OA reads 82v

Could you help me understand what might cause these high and low readings?

 

[Paul Birkeland]

What are the voltages on pins 3 and 8 with this one?

OA at 82V isn't a problem. OB at 142V would have me wondering if both halves of the 12AU7 are glowing. If not, there may just be a little corrosion on pin 4 or pin 5 of the tube, which would prevent one half from conducting. This may not have been an issue in the 9 pin socket of our tube tester, but could be an issue in a different tube socket like the ones we provide in the Crack.

 

[Jimb0]

Pins 3 and 8 both read 1.56V

Today at OA it's reading 115V and 135V at OB. Both sides of the tube appear to be lit.

If it's corrosion, is there anything I can do about it?

 

[Paul Birkeland]

Pulling and inserting the tube a few times will generally scrape off the corrosion. 115V is miles from 82V in this scenario. Was there anything different between how things were setup between when these measurements were made?

 

[Jimb0]

Nothing has changed, except that I’ve been running the unit for several hours yesterday and today with another tube.