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Post subject: Biasing SF Fender Champ with 6L6?
Posted: Sat Dec 03, 2011 8:59 pm
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Hello, all. This might be a dumb question.

I picked up a '73 Champ a couple of months ago and was so excited about the fact that I found anything vintage in my local store that I placed it on lay-a-way without really checking it out. Party foul #1, I know. :oops:

When I finally got it home it played just fine like it did when I tried it out in the store, but I couldn't get it to break up for the life of me. This is a little Champ, I thought, there's no reason this thing should stay clean all the way to 10.

So I got to looking at its innards and saw someone had replaced the 6V6 with a 6L6. I know this isn't uncommon, but I figured I could still get breakup with the 6L6 in there, right?

From the research I've done, it's my understanding that there's no need to bias if it's running a 6V6. Is this the case with a 6L6 instead? Or perhaps the tube is worn out or in the process of dying? Something else I'm not considering/don't know about? I'm pretty poor so I haven't got the money around to buy another (good) tube to swap out and troubleshoot that just yet.

I'm obviously a noob when it comes to tube amps, so any information and mercy you might spare me would be much appreciated.


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Post subject: Re: Biasing SF Fender Champ with 6L6?
Posted: Sun Dec 04, 2011 12:51 am
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The single-ended Champ Amp is self-biasing, regardless of which tube is used in the output stage. Have you checked to see if the other tubes are the correct type for the amp? These small Fenders do not compress or break up quite like their larger push-pull bretheren -- like all silverfaces, they were designed to play as clean as possible. For more grunt and grit, try a pedal or two. I use a Fulltone OCD with my silverface Bronco.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Biasing SF Fender Champ with 6L6?
Posted: Sun Dec 04, 2011 3:48 am
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6L6 will be cleaner than a 6V6 in this amp.

Cathode biased amp need also a bias check. Those amp are often biased too hot . Old tube are tougher than modern one. If you put a modern tube , checking bias (resistor) is a must.


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Post subject: Re: Biasing SF Fender Champ with 6L6?
Posted: Sun Dec 04, 2011 2:02 pm
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When I run 6L6GC in an OEM 6V6GT single-ended amp, I raise the cathode tied resistor to 680-ohm, 12 watt WW. And the bypass cap to 100-200 mfd/100VDC. It puts the 6L6GC closer to mid-swing point with the 325-350 VDC applied to the anode. And gives the amp better bass.

YMMV.


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