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Post subject: Tube rattle, replacement and fix bias question(s)
Posted: Sat Jul 16, 2016 12:20 pm
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Hobbyist
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Joined: Wed Dec 18, 2013 5:19 pm
Posts: 75
I have a 4 month old '68 Custom Vibrolux. It came stock with the GT 6L6s. Developed a tube rattle and when I would put pressure on the glass at the tip of the tube the rattle would stop. Only happened on certain notes and frequencies. Anyway took the amp to an authorized Fender repair center and they changed out the tubes at no cost. Solved the tube rattle for a minute. So I am going to order some tube dampers from Herbies I think they are called. Regardless here is my concern. The tech replaced the GT 6L6s with JJs and said there was need to bias the amp and did not even check. Just swapped them out and sent me on my way. I took him for his word but cant help but to be a little concerned. I am guessing the amp is fixed bias. Should I be concerned? Also if I order a bias tool is it something I can do? Thanks


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Post subject: Re: Tube rattle, replacement and fix bias question(s)
Posted: Sat Jul 16, 2016 1:39 pm
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Joined: Fri Feb 05, 2010 4:31 am
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Location: Province de Québec, Canada
To adjust bias, there is no pot, if bias is wrong you have to change a resistor. It need a qualified tech.

Unless this tech have experienced a 68 Vibrolux Reverb with a JJ's tube, what he said look bulshit to me.


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Post subject: Re: Tube rattle, replacement and fix bias question(s)
Posted: Sun Aug 07, 2016 1:58 pm
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Joined: Mon Jul 16, 2007 7:28 pm
Posts: 126
Yes, you can adjust the bias on the '68 Custom Vibro.
Yes, it's weird (at least) that this "tech" didn't do this.
(Makes one question his bona-fides as an actual tech.)
Yes, I own a '68 Custom Vibro.
Yes, I had similar issues with noisy output tubes.
I replaced them, re-biased the amp, couldn't be happier.
Your amp, no matter what it came with or what you put in it, will probably be biased "cold". Even brand new tubes are no guarantee that you will even be able to bias to the "warm" side. Just my experience.
Yes, a bias tool will help.
As a seat of the pants adjustment, find the bias adjustment screw. Make note of its position.
Then turn it counter-clockwise. Does it sound better? Good.
(It's not rocket surgery.)
If you can't tell, take the amp to a real tech, and have him do it.
Play the amp before you take it home. Sure, there is math to tell you what is technically "correct". This does not always correlate to "sounding good". For example, some will say the bias tremolo in the '68 Custom Vibrolux sounds better with a colder bias.
Good luck!


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Post subject: Re: Tube rattle, replacement and fix bias question(s)
Posted: Sun Aug 07, 2016 6:13 pm
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Aspiring Musician
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Joined: Tue Nov 27, 2012 9:07 pm
Posts: 604
Go To Eurotubes https://www.eurotubes.com/store/pc/how% ... videos.htm and watch the BIAS video's on Fender Amps. Most all classic Fenders look similar inside. So choose one of the videos as close to your amp as possible.

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If it sounds good it is good.
http://www.soundclick.com/bands/default ... tent=music


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