Weird sound when shutting of RCA 56X
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This a strange one. All caps replaced resistors checked, replaced as nec. Tube test ok. Radio aligned and sounds great. Just one thing. This sound when I shut it off. Any ideas?
Check it out: http://youtu.be/GE-8t0KIIJM
Schematic: http://www.nostalgiaair.org/Resources/991/M0014991.htm
Thanks,
Eric
Eric
The Villages, FL
Member: Philco Phorum, ARF, ARCI & Radiomuseum.org
(This post was last modified: 04-21-2013, 10:18 PM by Eric Adams.)
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I think it reminds me of a microphone effect.
Look for anything that can resonate at this frequency.
A tuning cap, tube.....basically it looks like the power switch introduces a quick jerk annd then something resonates at the frequency you hear.
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Thanks Morzh, I'll check those things. Have you ever had this problem? Do you think it could be caused by the switch?
Eric
Eric
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yes it potentially can be the switch itself if it bounces a lot.
here's the test (somewhat dangerous...that is requiring observing some safety, so be careful. Use an isolation transformer and never hold two wires or a wire and the chassis with both hands at the same time....you know the spiel);
Desolder one wire to the switch, turn the switch on and keep it on, so you can have the volume where it works, and use that desoldered wire to make/break connection. If the sound persists, it is not the switch, if it goes away - it is the switch.
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Well Morzh, it looks like it's the switch. My deoxit order should be here on Thurs or Fri. I'll get back to you after I treat it.
Thanks,
Eric
Eric
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You're alive, that's a relief. 
Deoxit is a good stuff but it may not necessarily cure the problem: if the switch has an excessive bounce Deoxit won't do a dang thing about it. It is mechanical. Then again, if this is the extent of your problem, it's nothing really bad.
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Yup! Gotta keep one hand in the pocket!
I'll try the Deoxit before I take the switch apart.
Thanks,
Eric
Eric
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I have one of those, your set is prettier, mine does not make that sound. Actually for a small set they perform quite well. I DX on it sometimes.
Paul
Tubetalk1
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Thanks Paul, it took a lot of cleaning and polishing. I haven't got my Deoxit yet and from the testing I'm sure the problem is in the switch. If I put pressure on it and shut it off there is no noise.
Eric
Eric
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Yup, just about always that. Causes a transient that briefly saturates output transformer above its limit to suppress such stuff. Best fix it lest you looking for new iron.
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Hey Morzh,
That did it. Just a little spray into the control and...no noise.
Thanks,
Eric
Eric
The Villages, FL
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Yup! Probably has hsppend to most of us.
(This post was last modified: 04-26-2013, 02:04 PM by codefox1.)
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Great! Well, dirt also causes bounce. Obviously.
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