Tube Bias

Ben
I'm not the one to answer this but I've never known biasing to effect volume.  Whether the amps biased hot or cold effects more tone and response than it does volume. How are the output tubes? Did you check all cables/connections? Are the tubes seated firmly?

Other than that...can't help you.  I may even be wrong with the above info.  Let us know what happens.  I'm always curious about this stuff.  Especially 'cause I'm looking to retube my Fuchs here shortly and I'm nerrvous about the biasing.

Ben...this is from the man himself as you know.  Thanks Don. 
I didn't know that.
Don, What are the Variables with biasing an amp.  In other words what are the ranges say from cold to hot?  How much play is there before it's TOO hot or TOO cold.
I know you do the Cat 5's but say in a Fuchs...any opinions? 
When I get it done I will call Andy...I play too much to ship the amp back to Fuchs to have it done but like I said...I'm nervous.  I want it to be perfect!

Thanks.
Danny

Woops hit send to early - Thanks Don.  What I have is a Top Hat Emplexador and It seems to break up way to early on what is basically a early plexi channel, even though its cranked, and it also doesn't seem loud enough.  I've played a lot of louder amps than this, and I hate having to turn down all my other amps, for this one to be heard.  Any suggestions?

Ben

Most techs set bias between 60-70 of the tube rating.  THis is dependent on the b+ voltage, so you have to cross refernce the tube with +B to get the correct bias max, then take 60-70 percent of that.  Colder gives you a lillte more tube life.  Too cold and it will sound sterile, too warm and it will sound too aggressive.  Some of this is to taste of course.  We had a 68 JB head that sounded great but not loud enough, check the bias-on the cold side.  put it in the range above-back to normal.

I'm not the tech in our company, but this should at least help you know what to expect.  The manufacturer should tell you.  FYI our 100 watt el34 JB 68-100 biases at 37mA.

DonR

Ben, bias simply refers to the amount of current going through the power tubes so they work at peak effiency.
An amp that's biased cold will not have as much current as the tube manufacturer's specs call for and will usually sound a little grainy or " cold " when pushed. They can also sound a bit spongy at lower volumes and some players like this especially in older fender amps. Some players also bias a little on the cold side to make their power tubes last a bit longer.
Biasing hot increases the current to the power tubes and increases the gain factor. The tube runs on the hot side and can sound like it's being pushed earlier.
This works better in marshalls where a more aggressive type of gain is usually required.
When you buy a certain brand of power tube the manufacturer will have specs that show what the tube's optimal bias current should be. That's an average bias may or may not be right for your ears.
I would bias to the manufacturer's specs and then go up or down, depending on the tone you like best while keeping within range of the power tube's abilities.

Just on a side note, biasing, while it can increase gain, will not affect your amp's volume to any real extent.
It may seem a bit louder if you bias hot because the tubes gain cuts through in a different way but there is no real power difference.
Changing the brand of tube manufacturer may give you a slight increase or decrease in power as well as headroom and changing the type of rectifier tube can give you a noticable difference in power because the type of rectifier will increase or decrease the amp's wattage.
If you're not sure about biasing I'd let a tech do it for you. If you have a bias probe and are comfortable with it then it's not a big deal and it's probably a good thing to learn.