COLD BIAS?????? v TONE??????

[OlinMusic]

A lot of people have told me about amps being biased a little cold, so they raised the bias to match the tube type, etc etc

What I want to know is - say you have a Marshall, Bogner, Mesa, Fender et al and it's biased cold, how will the tone change when you warm it up?

What about the cold biasing makes it undesirable and how does the warm bias change things?

(I have my own ideas on this, but I want the opinion of an amp guru, por favor)

 

[ModestCargo]

Re: COLD BIAS?????? v TONE??????

I'm sure you've sort of figured it out already - cold biasing will give you more headroom and the sound will be "cleaner", but you will lose some warmth, and of course some like an early breakup point anyways.

 

[STRATDELUXER97]

Re: COLD BIAS?????? v TONE??????

With a hotter bias(More current going through the tubes)your tone is ballsy,fatter,stronger,more direct,but you lose the clean headroom...

 

[Gearjoneser]

Re: COLD BIAS?????? v TONE??????

I think if a tech puts an oscilloscope on the circuit, there's supposed to be a Q point where there's no crossover distortion on the sine wave.
I've always done it by ear with my eye on a mA meter, using a mA bias tool.

To me, the amp is biased when it sounds as rich, bold, and tight as possible, which is probably right near that Q point. I just stay around 32mA for 6L6 and 38mA for EL-34's, give or take a couple of mA. The difficult part is juggling the guitar so I can strum it, while turning the bias pot on a live amp without electrocuting myself! There's no room for error, so I keep my left hand off the strings, and always have a glove and plastic handled screwdriver on my right, then I listen as I make tiny adjustments. I usually prop the chassis up with books under the transformers, so it can sit with the circuitry face up.

 

[STRATDELUXER97]

Re: COLD BIAS?????? v TONE??????

I think if a tech puts an oscilloscope on the circuit, there's supposed to be a Q point where there's no crossover distortion on the sine wave.
I've always done it by ear with my eye on a mA meter, using a mA bias tool.

To me, the amp is biased when it sounds as rich, bold, and tight as possible, which is probably right near that Q point. I just stay around 32mA for 6L6 and 38mA for EL-34's, give or take a couple of mA. The difficult part is juggling the guitar so I can strum it, while turning the bias pot on a live amp without electrocuting myself! There's no room for error, so I keep my left hand off the strings, and always have a glove and plastic handled screwdriver on my right, then I listen as I make tiny adjustments. I usually prop the chassis up with books under the transformers, so it can sit with the circuitry face up.

That's Doctor GJ.....:laugh2: