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Topic: Showman Dual Reverb feedback |
Jason Williams
From:
Seattle, Washington
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Posted 1 Feb 2010 12:01 pm |
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| I've been having this '69 FSDR head overhauled to use for steel and have run into all sorts of fun surprises. Most recently, when I turn the reverb past 4, the loudest feedback I've ever experienced occurs. I thought it might be the reverb circuit tube, so I switched it out, and now it only happens intermittently. I want to continue to use this amp playing out, but I don't want to feel like I'm playing Russian roulette every time setting my levels. Anyone else have any problems similar to this? |
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Clyde Mattocks
From:
Kinston, North Carolina, USA
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Posted 1 Feb 2010 1:35 pm
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I would guess the tank has become microphonic. You might try stuffing a heavy towel or other piece of fabric over the reverb tank to see if you can interrupt the oscillation between it and the speaker. Also try changing the small reverb send and recovery tubes. You will probably end up having to replace the reverb tank itself. They are not terribly expensive. www.newsensor.com has them.
_________________
LeGrande II, Nash. 112, Fender Twin Tone Master, Session 400, Harlow Dobro, R.Q.Jones Dobro |
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Ken Fox
From:
Nashville GA USA
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Posted 1 Feb 2010 5:17 pm
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| Replace the 25uf cap at the cathodes of valve 4, the reverb return and wet/dry mix gain stage tube. |
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Rick Johnson
From:
Wheelwright, Ky USA
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Posted 2 Feb 2010 11:41 am
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Jason
This may sound silly but sometimes
guys take the reverb tank out and
get it turned around backwards when
they put it back. This can cause
it to squeal. Facing the rear of the amp
the leadwires coming out of the reverb bag
should be to your right, ot the normal
channel.
Rick
www.rickjohnsoncabs.com |
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Ken Fox
From:
Nashville GA USA
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Posted 2 Feb 2010 6:18 pm
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| I have fixed this same problem over and over in Fender amps. Unplug the reverb tank cables at the amp Now turn up the reverb control. If it still feeds back that cap is bad |
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Jason Williams
From:
Seattle, Washington
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Posted 2 Feb 2010 6:30 pm
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| Thanks for the input Gentlemen! |
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Clyde Mattocks
From:
Kinston, North Carolina, USA
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Posted 2 Feb 2010 9:33 pm
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Thanks Ken, I learned something there !
_________________
LeGrande II, Nash. 112, Fender Twin Tone Master, Session 400, Harlow Dobro, R.Q.Jones Dobro |
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Ken Fox
From:
Nashville GA USA
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Posted 3 Feb 2010 5:18 am
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| When that cap goes bad it will put the amp into oscillation at about 1K hertz at full power. It will wake up the dead!! |
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Jim Sliff
From:
Lawndale California, USA
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Posted 3 Feb 2010 7:01 am
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What Ken and Rick said.
On SF/BF reverb amps I automatically replace that cap if it's original. And I can't even count the number of times I've "serviced" an amp over the phone with a reverb tank reversed.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
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