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PostPosted: Fri Jan 02, 2009 8:59 pm 
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Mark II

Joined: Wed Aug 15, 2007 3:57 pm
Posts: 63
I swapped out the EL34's that I had in my LSC with 6L6's and forgot to switch the bias switch. I only ran the amp a couple of hours. I was noticing the tone was weak and that's when I discovered the problem.

But I also noticed that the 6L6 nearest the Rectifier tube was running totally cold and had a gassy coating at the top. Would the incorrectly configured bias have caused this? Or perhaps I have a bad power tube and IT was causing this symptom.

Also, would the misconfigured bias switch cause any longer term damage to the amp?

The amp seemed to be running fine after I corrected the bias, even with the one cold tube. I figure this is probably because I ran the amp at 50 watts which I understand only runs the two inner power tubes.

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PostPosted: Sat Jan 03, 2009 10:06 pm 
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i think the 50 watt mode runs the two outside tubes.

...not sure about the damage question, but i think any significant damage would be pretty obvious.
If it sounds ok now, i think you got lucky.



gregrjones wrote:
I swapped out the EL34's that I had in my LSC with 6L6's and forgot to switch the bias switch. I only ran the amp a couple of hours. I was noticing the tone was weak and that's when I discovered the problem.

But I also noticed that the 6L6 nearest the Rectifier tube was running totally cold and had a gassy coating at the top. Would the incorrectly configured bias have caused this? Or perhaps I have a bad power tube and IT was causing this symptom.

Also, would the misconfigured bias switch cause any longer term damage to the amp?

The amp seemed to be running fine after I corrected the bias, even with the one cold tube. I figure this is probably because I ran the amp at 50 watts which I understand only runs the two inner power tubes.

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PostPosted: Sat Jan 03, 2009 10:49 pm 
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Location: Greenville. SC
I did this once...

viewtopic.php?f=4&t=26937&p=199405&hilit=oops+el34+switch#p199405

Basically, running EL34s with bias switch in 6L6 would be bad, but running 6L6s with bias switch in EL34 will just sound bad... if it sounds OK then you should be fine.

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PostPosted: Sun Jan 04, 2009 12:20 pm 
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Mark II

Joined: Wed Aug 15, 2007 3:57 pm
Posts: 63
YES I lucked out because I was running the 6l6's with the EL34 setting, NOT the other way around!

Now, my question is: Did this kill the tube?

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PostPosted: Thu Feb 05, 2009 6:49 pm 
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Single Recto

Joined: Thu Jun 14, 2007 7:34 pm
Posts: 1164
Probably. The EL34 setting is a lot hotter than the 6L6 setting on the bias switch. I did this once and my amp had to go into the shop for fried grid resistors. EL34's in the 6L6 mode will sound like cow pie, but slim to none for damage. After doing this, I made a habit of always checking the bias switch before turning it on.
A good test is to check out the clean channel on 50 watts. Mine sounded weird, kind of half-phase or underwater.

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