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bubbleboy
PostPosted: Wed May 16, 2007 10:06 pm 
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Do you have to bias the EL84's on the slll?
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coco
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PostPosted: Thu May 17, 2007 9:06 am 
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Nope. Tthe 18, 15 and Deluxe are all cathode biased. No set up required. A common power resistor on the power tubes cathodes sets the bias.

In contrast, a JTM45 does requires biasing making that build more complex.

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Wicksy
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PostPosted: Mon May 21, 2007 9:08 am 
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As a side note i have found that you need to keep an eye on your power tubes. The Ampmaker 18 watt lite i built took JJs fine with the 150R cathode resistor but when i tried NOS Polam EL84s, there was a little red-plating under low light conditions. I upped the cathode resistor to 180R and had no further problems.

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zaphod
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PostPosted: Mon May 21, 2007 9:12 am 
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Or you could have made sure not to use your amp in low-light conditions. :lol:

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coco
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PostPosted: Mon May 21, 2007 9:13 am 
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Safe advice. We have used 125 ohm OK so far.

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rjgtr
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PostPosted: Mon May 21, 2007 2:47 pm 
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Of course they still red plate in bright light conditions, but tubes always sound great when they are dying! :lol:

So a few minutes of bliss might be worth changing tubes every song! :roll:

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