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Old 1st June 2006, 07:59 PM   #1
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Default Bias Check As Preventive Maintenance?

Should I check and adjust the bias (via voltage across emitter resistor) on my amps as a preventive measure or leave alone until I have a problem? I don't want to tamper with the adjustment pots if not absolutely necessary, I am guessing this could be a problem with pots that have stayed set for 30 years (ie vintage receivers), is this the case? Are these pots cleanable like other controls using Deoxit, is this a good thing to do while I have the unit open doing other repairs on a typical unit?
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Old 1st June 2006, 10:16 PM   #2
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Unless you have the manual or know how to set the bias I'd leave it alone if the amp plays fine. If you plan to give it a major maintenance you could consider replacing the pots and some or more caps.

/Hugo
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Old 1st June 2006, 10:25 PM   #3
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Hi DreadPirate,
I'm with Hugo on that. It would not hurt to record the values and leave them on the inside. Turn it on and let it idle for 20 min. with no load or signal first.

Yes, if you need to adjust the old control, you can clean the slip ring and contact with deoxid. Work the control a little and it should be fine. There will be a small indent you can feel in the position it has sat for so long in. Start there if you need to adjust it.

-Chris
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Old 1st June 2006, 10:32 PM   #4
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I would have to say to stay clear of it because I have repaired to many amplifiers that some one thought they were going to tweek the bias and the pot was bad. I don't need to tell you what happened then.
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Old 1st June 2006, 10:38 PM   #5
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The current meter went up and they turned it off in time?
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Old 1st June 2006, 10:42 PM   #6
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The current meter went up and they weren't expecting that to happen. Therefore by by output stage.

I told them not to trust an old bias pot. Did they listen to me? Nope....
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Old 1st June 2006, 10:52 PM   #7
anatech is offline anatech  Canada
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Hi Joe,
That's how all young people learn.

-Chris
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Old 1st June 2006, 10:57 PM   #8
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Chris,

Not sure if us older people can take the strain.
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Old 2nd June 2006, 12:33 AM   #9
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There is alot to be said about not screwing with things that appear to be working and I wish I heeded my own advice a thousand times in the past, but shouldn't I at least measure the bias and see if it is close to what the manual says? Or am I just tempting myself into disaster?
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Old 2nd June 2006, 02:05 AM   #10
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Hi DreadPirate,
Go for it. Carefully.

Hi Joe,
Quote:
Not sure if us older people can take the strain.
Yeah, I'm all burned out.

-Chris
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