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Old 12th October 2010, 07:11 PM   #1
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Default ARC LS25 mkII tube change

I am thinking of replacing the 2 6H30 tubes. Is this swap and play or do I need to adjust the 2 trimmers on the board? The manual says nothing about this.
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Old 15th October 2010, 03:56 PM   #2
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No one knows? I imagine I am supposed to measure someplace and set the trimmer to a specific voltage...
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Old 15th October 2010, 04:18 PM   #3
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just plug & play

trimpot is for Jfets operation
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Old 15th October 2010, 04:31 PM   #4
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Originally Posted by Zen Mod View Post
just plug & play

trimpot is for Jfets operation
Thanks for your response.

Can you tell me how to make sure the trimmers are adjusted correctly? I assume I am supposed to measure some location on the board and check for a specific voltage?

I got the preamp 2nd hand so want to make sure everything is good.
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Old 15th October 2010, 05:09 PM   #5
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just check +/20V points

re- set with pot if needed

but - if nobody didn't tweak them , they're probably fine
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Old 15th October 2010, 05:20 PM   #6
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Originally Posted by Zen Mod View Post
just check +/20V points

re- set with pot if needed

but - if nobody didn't tweak them , they're probably fine
Thanks so much! Exactly what I needed.

The previous owner told me John Rutan of Audio Connection did the tube change couple of years ago. And perhaps he messed with the trimmers...

I want to make sure.
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Old 18th October 2010, 04:09 PM   #7
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Did a voltage check throughout the amp. All looks good. I had to tweak one of the trimmers a very small amount.

The preamp sounds great to my ears.
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