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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: How do I set the bias? posted by CMan on September 10, 2003 at 11:57:48:
Hi,I've got an X-100 as well. Haven't refurbished it yet but I will sometime down the road. Here's a link to a schematic I found on the web:
http://intra.engr.uark.edu/~lar/fireamps.html
My amp appears to be the same as this one, perhaps your's is as well. I'm no expert, but I would recommend installing the resto-kit before you power up the amp unless you know for a fact that the caps are in good shape. Was the amp up and running when you purchased it? If possible, bring it up slowly with a variac.
According to this schematic you need to adjust the bias pot so that the cathode (pin 3 on any of the el84 tubes) reads 40 volts. To make this measurement set your voltmeter to read DC volts. With the amp off, attach the black probe to the chassis at some point and attach the red probe to pin 3. Now you can turn the amp on. Turn the bias pot until it reads 40 volts and NOT any higher. I don't know your knowlege level so I have to say "be careful!" There are lethal voltages involved here.
How stable will it be? If the caps are fresh I'd say check it once a year. Personally, with an amp this old I would replace the caps to be safe. Good luck!
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Follow Ups
- Re: How do I set the bias? - microbe 20:22:32 09/10/03 (1)
- Re: How do I set the bias? - CMan 20:50:43 09/10/03 (0)
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