"Cold" bias? "Hot" bias?

[Mike M.]

I understand the need for an amp to be biased but I'm not real sure what is meant by cold vs. hot bias. What effect on an amps tone would either/or have? Thanks.

 

[That90'sGuy]

Cold bias is when its set lower, Hot bias is... you guessed it, when the tubes are set higher.

 

[Scott_F]

Like an idle on a car engine. Too high an idle, you burn too much gas (kill off tubes too quickly), car lurches into gear (goes from quiet to raging distortion too quickly).

Too low, the car stalls out, but man does it save gas!

 

[Mike M.]

So if I'm understanding this correctley, if the bias is set to hot the distortion will be too harsh, and if the bias is set to cold the distortion would be rather wimpy? Is this right?

 

[y2stevo]

i think itsmore like if you set the bias cold you will have much more headroom, that is more volume before it starts to break up, then hot is the opposite, hots better if you want cranked quality tube distortion at lower levels..

 

[Wattage]

Too cold it might not make much sound at all.

Eurotubes FAQ

 

[Gearjoneser]

You can bias by ear. When the amp sounds boldest, punchiest,
and the most healthy, it's probably where it should be.

To cold. The distortion sounds grainy and feeble.

To hot. The normal sound of the amp is TOO pushed sounding
and it lacks boldness. Get's kinda squishy sounding.

 

[proxy]

Hot means you are running more voltage into the tube. More voltage will mean the tube will heat up more and distort more. It will also shorten the tubes life somewhat.

And obviously Cold would mean lower voltage to the tube, not pushed as hard so its cleaner, not as hot physically, and longer life.

 

[Naps]

Too cold it might not make much sound at all.

Eurotubes FAQ

Cool. Thanks for the link.

 

[Mike M.]

Thanks all. All this pertains to my Hughes and Kettner Tube 50 combo. I plan on having JJ's installed and was trying to figure out if the amps bias is currectley set to hot or cold. Nasty kind of distortion. Too much distortion too soon from the amps distortion channel. Has a very harsh, "barky" kind of sound to it.

 

[Pandemonium]

To cold. The distortion sounds grainy and feeble.

Exactly. I put new power tubes in my JCM 800 last year and thought I'd just see how it sounded before I had it biased. It sounded thin and raspy, really crappy. The tech set it was biased way to cold for those tubes.