I don't want to do this here, but I've nowhere else to go!

[mukuzi]

I have a Fender Champ 25 that I bought pretty much on impulse. I really like it.

 

I replaced the power tubes in it, and it sounds better. Trouble is I have no idea if it needs to be biased or not. I can't find any information on it on-line, and I'm too stupid to understand the schematic.

 

I know the Champ 12 was cathode biased.

 

I'm too afraid to admit to the amp forum that I own an amp under 10000000 Watts.

 

Will you help?

[NoirAbattoir]

Hmmm... The fender amp field guide doesn't seem to know, either:

http://www.ampwares.com/ffg/

In the bias category for that amp is a big "?."

[jonny guitar]

Champ 12 was only one tube so it didn't need the bias adjustment...I am not sure about the 25 but my gut says no need.

Can you see a bias pot in there when you pull the chassis?

[Fxrs]

Ask over at TGP.

[jonny guitar]

Originally posted by Fxrs Ask over at TGP.

[mukuzi]

Originally posted by Fxrs Ask over at TGP.

I'd sooner let the amp burn itself out.

I've decided to not worry about it. If it dies on stage at least everyone will be spared from having to hear me play.

[jb1911]

I checked the schematic:

http://www.schematicheaven.com/fenderamps/champ_25_se.pdf

and the cathodes (pin 8 on the 6L6s) are directly grounded. That means it is NOT cathode biased and it DOES need to have it's bias adjusted with each tube change.

Hope this helps.

By the way, the absolute best place to ask questions like this is the Fender Discussion Page:

http://www.fenderforum.com/forum.html?db=

[RoboPimp]

I bias my tubes every 5000 miles

[Ronsonic B]

Let's look at this from a practical aspect:

If the amp is biased too cold it will hurt the sound. Set the tone controls for something normal in the middle of the travel, turn the master volume up if you've got one, turn the gain / volume control up to something like 2. Just loud enough to hear clearly in a quiet room. Strum some big open chord, like a G, and listen. Is it smooth with an even long sustain and decay? if so it isn't too cold.

If it is biased too hot you'll overheat tubes and damage them or the amp. Power up with the amp turned away from you and watch the power tubes. You'll see the heater glow, but there should be no glow or red color on the plate (the large gray stamped structure that fills most of the tube). Turn it up and jam! Pound it good, this is a good time for your Ramones tribute. Watch the tubes, any hint of red is bad. Otherwise not so bad.

If you pass both of these tests - all is probably well.

Now go to somebody like STF electronics and buy a bias probe kit and do it right. But you won't blow anything up in the meanwhile.

Ron

[jb1911]

Good advice, Ronsonic B. I find that too many people are way too anal about biasing. I care more about the tone than how long the tubes last, but that's all up to the individual. Some people don't care about anything.

[mukuzi]

Thanks!

jb1911, I really appreciate the fact you checked the schematic. I'm touched.

I'll check the amp after work, and see if anything is redder than it should be. If I have to play loud, so be it!