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Why wont this Little Bear t11 work with 12ax7s?

Moonwatcher

Moonwatcher

Active Member
Hello, all,

I have a Little Bear T11 that I accepts either 6n2 or 12ax7 tubes. There is a switch next to each tube for picking one or the other. The stock 6n2's sound fine, but I wanted to try vintage 12ax7s that I'm pretty sure worked last time I tried them. But not a single one of them lights up, and there is of course no sound.

Would it be OK to try switching to 6n2 for just a few seconds, with the 12ax7s still plugged in, to see if the current even switches over? Any idea what could be causing the problem? Another change needs to be made before flipping the switch over to 12ax7?
Thanks!

P.S. As others have said, putting the metal shield on the far left tube and grounding it definitely minimizes the hum.
 
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So, putting 12ax7's in and setting the switches to the 2ax7 gets you no heater glow? I can't remember if it's wired series or parallel for heaters in this one. If it's series an open heating element in one tube could cause all of the heaters to not pass current. Try each of 12ax7's at a time in one socket set to 12ax7, and use two 6n2's in the other two sockets set to 6n2.
Maybe you just have one bad 12ax7? You accidentally run one or more 12ax7's set to 6n2 maybe and roasted a resistor?
 
Great idea, about using two 6n2's set to that and trying the 12ax7s one at a time. (I wasn't sure that was an option.) I don't think I ran them on the wrong current or roasted a resistor. It sounds fine with the originals. Thanks!
 
Hopefully it's just a bad 12ax7. I have a T-11, the first tube is the most important for how it sounds.
 
Thanks again, Lavana, because after trying the 12ax7s one by one with the other two 6n2s, each one lit up, and when I put them all back all of the 12ax7s worked. Not only that, but I did not even need to ground the cover of the first one. Little or no hum. And I have to say it sounds better than ever with these vintage GE (I think) 12ax7s!
 
Glad you figured it out. Those GE's should sound better. I have a bag full of 6n2's and none of them sounded very good and some are very microphonic.
 
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