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Old 22nd April 2017, 03:24 PM   #1
kendt is offline kendt  Canada
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Default Odd issue with first turn-on

I wondered if anyone might be able to assist with a problem in my new build. When I first turned it on to test voltages after a few seconds i started to hear a clicking sound and noticed some minor sparking between some of the pins of the 6p15p output tube. Its not any serious zaps just very light. I was thinking that maybe the bypass cap might be funky but i thought someone else has encountered this and could shed some light on it before I start pulling parts out.

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Old 22nd April 2017, 04:02 PM   #2
Ketje is offline Ketje  Belgium
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SE amp without speaker connected and motorboating ?
Mona
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Old 22nd April 2017, 05:15 PM   #3
kendt is offline kendt  Canada
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well i have had motor boating with other builds and never had sparks or clicking sounds. I tried reversing the tubes but it didnt change.
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Old 22nd April 2017, 05:54 PM   #4
kendt is offline kendt  Canada
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Quote:
Originally Posted by Ketje View Post
SE amp without speaker connected and motorboating ?
Mona
Ok well it appears you were right.I connected speakers and the sparking went away.It is motorboating but also making some screetchy crackling noise. Very frustrating indeed.
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Old 22nd April 2017, 06:22 PM   #5
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Sounds like positive feedback.
Is the feedback connected in the correct phase ?
You can try reversing feedback + and - to see if that is the problem.
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Old 22nd April 2017, 06:22 PM   #6
Ketje is offline Ketje  Belgium
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Well, sparks can make short circuits within the OPT.Also damage isolation between pins.Perhaps a capacitor over the primary of the transformer didn't survive.
Mona
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Old 22nd April 2017, 07:15 PM   #7
DF96 is offline DF96  England
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Could be HF parasitic oscillation (possibly at OPT HF resonance?) due to lack of damping from speaker. You are fortunate that you did not blow the OPT. Never, ever, run a valve amp with no load attached.
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Old 22nd April 2017, 08:26 PM   #8
kendt is offline kendt  Canada
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Thanks.Ive done it in the past and never had an issue.Got lucky I guess. I moved the ps ground to a point on the chassis and everything settled down all except for a very slight hum.
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Old 22nd April 2017, 08:36 PM   #9
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NEVER EVER POWER ON A TUBE AMP WITHOUT LOAD!!!
It is possible to protect output transformers in PP amps by reverse-parallel to tubes damper diodes, but you can't protect SE transformers so simply!
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Old 22nd April 2017, 08:38 PM   #10
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Quote:
Originally Posted by DF96 View Post
.Never, ever, run a valve amp with no load attached.
Like he said, *NEVER EVER*. Yes, you've been extremely lucky so far.

Sent from my phone with Tapatalk. Please excuse any typpos.
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