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| | |-+  Can anyone tell me what the trim pot between the two 6L6 pots does?
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Author Topic: Can anyone tell me what the trim pot between the two 6L6 pots does?  (Read 7891 times)
Adam
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« on: June 04, 2009, 02:29:05 PM »

Hi, I just received my OTS. Tone is great. I thought I would go with the internet chat about trimming down the OD by adjusting the trim pot. I looked in the back, saw one pot and went for it. I've just learned that you have to remove the chasis in order to get at the trim pot. So, now I'm wondering what I've done to my brand new amp. Can anyone tell me what that pot does? The pot I adjusted is the only obvious pot as you look into the back of the amp, without removing any screws, between the two 6L6 tubes and a little behind them. Thanks, much appreciated,

Adam
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docmh
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« Reply #1 on: June 04, 2009, 02:48:13 PM »

That is to adjust the bias for the power tubes. Nik told me it should be set for around 35 mvolts.  There's some info in a Dec. 31, 2008 overtone forum thread, "Noob manual on biasing" about how to do this. I don't know how to send it to you, so you'll have to look it up.
Hope that helps.
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Adam
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« Reply #2 on: June 04, 2009, 05:01:57 PM »

Thanks for your info, it does help. At least I know what the problem is. Guess I'll buy one of those meters and learn a new skill. I'll look up that post. Thanks,

Adam
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docmh
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« Reply #3 on: June 05, 2009, 01:28:51 AM »

Hi Adam,
    Just in case you didn't get a chance to look that thread up or try it yet, I tried it myself today. It's easy. I set my meter on the DCV scale at 200m. On the chassis between the tubes are 2 red and 1 black tiny inputs. I plugged the red meter leads (positive) in one of the red plugs and the black lead (neg.)in the black one.
Let the amp warm up awhile and you'll see the voltage on the meter. adjust the trim pot til you get your setting. Be careful, the potentiometer is not easy to get at behind those really hot tubes, I've really burned myself on hot tubes before. After you adjust the ist tube move the meter lead to the other red input and adjust the other tube. It's rare that they both read exactly the same even if they're a matched set. One of my tubes shows 34mv and the other 36. Good luck!


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