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Old 21st November 2008, 02:55 AM   #1
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Default Tubelab SE oscillation?

My Tubelab SE has been doing well since replacing FRED diode with Fairchild's "stealth" diode however, I've been noticing faint buzz from my speakers. When I turn the amp on, it's very quiet. Then about 5 minutes later I can hear "tic" at about 1 second interval. Then the pace picks up gradually and in about 20 minutes or so, it becomes buzzing sound. It's not loud but it concerns me because it wasn't like that before. Is this an oscillation?
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Old 21st November 2008, 03:07 AM   #2
m6tt is offline m6tt  United States
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I've had the ticking happen in guitar amps (which did not have vibrato, although that'll sometimes tick). It was coming from nearby electronics, in my case, although it may have been coming in through the mains. I moved, and the problem stayed behind, thankfully. What kind of source are you using? If I connect one of my computers as a source to one of my amps, I get horrible ticking as well as radio frequency detection. I thought it was my amp for a long while, until I plugged the computer into some commercial equipment I have and it does the same damn thing, albeit a bit fainter. Have you tried flicking the tubes to check for microphonics?
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Old 21st November 2008, 06:52 AM   #3
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My 300B tubes are microphonic no matter what. These are the same tubes I had when it didn't buzz and the tubes are new. Could a power cord near by cause this ticking gradually turn into buzzing?
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Old 21st November 2008, 05:18 PM   #4
Zap is offline Zap  United States
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It sounds to me like an oscillation that begins very slowly and eventually runs away, turning into a buzz. Is the only thing that was changed the diode(s)? I'm gathering if they were a pair before, you've likely replaced them both, as that could have an effect.
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Old 21st November 2008, 05:24 PM   #5
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Quote:
Originally posted by Zap
I'm gathering if they were a pair before, you've likely replaced them both, as that could have an effect.
They were a pair and I did replace both. Do you mean one or both could be defective? I checked both with multimeter before installing. Are there some other properties that can come into play?
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