biasing your amp

...or rebiasing, depending on your point of view.

anyway - this is something that you should only do if you KNOW WHAT YOU'RE DOING. Your amp has big capacitors in it like old TVs that can hold a charge long after you've unplugged your amp, and that charge is enough to KILL you if you're unlucky. so don't do it unless you've been shown how to properly discharge them. if you don't want to do it yourself, i can do it for you ;-) if you're brave enough to think about trying it though, read on...

that being said - most of what i can say about it has already been said here, but i can add a few additional pointers.

#1 - if you check the amp's bias current several times over the first 15 or 20 minutes it's been on, it'll continue to creep up - so to avoid biasing too hot, you're probably better off letting it warm up that long before taking a measurement.

#2 - the ted weber bias-rite is a handy little device, especially if your amp doesn't have a bias point built into it - but i've found that the reading coming off of a single "head only" bias-rite (the thing that just has leads coming off to plug into a stand alone multimeter) seems to be a little low - at least when dealing with an amp with more than one power tube. My guess is probably that the value at the plates doesn't quite sum to the value at the bias point, at least in the case of my deville - but it's something to keep in mind. Not sure how that compares to the actual 2 & 4 head bias-rite device...just keep this in mind - although you shouldn't be biasing at the absolute limit of the tubes anyway.

#3 - biasing too cold causes the amp to buzz and give you flabby lows. biasing to hot causes you to distort quick. both are bad for the tubes, and possibly the transformer. too hot is probably worse than too cold, though.

#4 - replace your power tubes after about 2 years of use if you use the amp 'regularly'. you'll be amazed at the difference in the sound. replace the preamp tubes every 4-5 years, or when they start to go microphonic. if you hear weird rattling when you play the amp, or weird out-of-key harmonics, that's microphony. chances are this is how your preamp tubes will go. they're relatively cheap, and don't need to be biased, so this is always a good first thing to do.

#5 - speaking of microphony, DON'T ROLL YOUR AMP ON BUMPY CEMENT if you have coasters on it. this is the quickest way to develop microphony and ruin otherwise good tubes. this is why 50-pound tube combos don't come with coasters on them.