If you haven't already, please observe the disclaimer atop http://www.justinholton.com/hotrod/bias.html, thanks.
First of all, you're going to have to bias the amp while it's on. So it's important to be very careful. You'll be fine as long as you don't touch something that you're not supposed to, or try to eat C10 because it looks like a cinnamon chicklit. I know, I know they taste sooo good. Don't try it! Just remember, you're dealing with a "live" 420V circuit and this is no joke.
A good rule-of-thumb is the aptly named "One Hand in Pocket Rule." The idea is to only use one hand at a time, leaving the other safely in a pocket. This will help prevent current from passing through our heart and killing us. Also, when our amp is on the power tubes will get very hot. If you accidently touch them they may burn you! Remember, you can always take it to a tech if you're uncomfortable—just look in the yellow pages under "Musical Instrument Repair."
1. You may lay the amp on it's front, or stand it up—whatever is the most comfortable for you. If you choose to set it on a table make sure it's sturdy. Stand on an insulated mat if you have one, especially if you have to do this in your basement! Wear shoes with rubber soles! Do not plug in your guitar. When we bias an amp we're setting the "idle," or the amount of current that flows while our amp doesn't receive a signal.
2. Remove the back panel. Many people think they need to turn all the knobs to 12 o'clock before they bias, this is a myth and doesn't affect the results. In fact, it doesn't matter how your tone controls are set as they only color the preamp and we're setting the working condition of the poweramp. However, since the back panel has been removed the amp will now be more susceptible to any interference—not to mention it's own heater supply. Therefore, the volume controls should be turned off to help minimize hum and interference from being amplified.
3. Turn your amp on and let it warm up. Look for the "Bias Pot," and the "Bias Test Point." (a.) The Bias pot (R82) is the blue circle with the notch in it. (b.) The Bias Test Point is naturally above the power tubes. It's on the corner of the circuit board, and is clearly marked. Get a screwdriver and turn the bias pot all the way to one side, and then the other. Now you have a feel for the pot. Adjust the pot so that it's right in the middle—this is a good starting point.
4. (a.) Place the black lead at ground (somewhere on the chassis). If you have probes with the alligator clip ends then clip it to the chassis, this is the safest method. If you don't have any, go to Radioshack or your local hardware store and get some. (b.) Flip your Standby switch so that the amp is active (off of standby). You'll probably hear a buzzing sound since the back panel is used to shield the circuit from interference. This is normal. Adjust your meter to read DC voltage, and place the multimeter's red probe on the Bias Test Point (the solder). (c.) Set your meter to its highest range. Adjust the meter's range down one range at a time until you can clearly see a reading. (d.) Use a small or medium sized flat-head screwdriver to adjust the bias pot. Turn the pot clockwise to bias hotter, counter-clockwise to bias colder. The bias pot should allow us to read roughly 50mV to 100mV at the bias test point. If not refer to the trouble shooting section. 68mV is considered a good starting point for beginners, and is approximately the point where a lot of people like to bias their tubes. Fender recommends adjusting to 60mV, but that's a little on the cold side based on the plate voltage of these amps. Note that 68mV is for 6L6GCs, and similar power tubes only. If you've installed an odd pair of power tubes, like 6V6s, use the biasing calculator to make sure you're not biased too hot.
If we've gone too cold we'll hear an annoying buzz clearly riding on low notes—this is crossover distortion. If we go too hot our tube's longevity will be shortened, and in extreme conditions a hole will melt into the glass of the tube. Remember: The hotter the bias, the shorter the tube's life, the lower the clean's headroom, and the hotter you run the entire poweramp. I personally recommend staying below 80mV for both the Deluxe and Deville. (e.) Can you guess what I'm doing wrong in this picture? If you said, I'm sticking both hands inside of a live amp you're correct! As stated earlier, a rule-of-thumb is that we should only stick one hand inside of a live amp, and leave the other hand safely in a pocket. Though it's not as obvious, if you said that I'm leaning over the power supply transformer you're also correct. If I tripped or slipped I could be seriously injured. Avoid these mistakes!
5. If you're a tweaker, and comfortable with biasing, try this step. Plug in your guitar into the power amp in input of the effects loop. This will exclude the sound of the preamp, though you can plug into the amp as normal if you'd like. As always LISTENING IS CRITICAL when finding a good sound. Playing at louder volumes may help you hear the differences better. SET YOUR GUITAR DOWN BEFORE READJUSTING THE BIAS! Remember: Your guitar's strings and bridge are grounded! If you go poking around the inside of your amp while holding your guitar in the one hand, and the other inside the amp, there's a chance you could have several hundred volts pass through your heart. This could very well mean death. As long as you use an insulated screwdriver to adjust the bias pot, and unplug your guitar from your amp, you'll be fine. If you're more experienced, and biasing by ear, be sure to use my Biasing Calculator to quickly calculate plate dissipation.
6. After you're satisfied, turn the amp off and screw the back panel back on. That's it! As I said, tubes need to be broken in, so if they're new I'd rebias in a week or so.
Q: The highest I can bias is (a very low number). What's wrong?
Q: The lowest I can bias is (a very high number). What's wrong?