Bias and tone

[Quencho092]

i know bias is key to good tone and tube life, but how exactly does it affect tone?

A cold bias, i think, would mean that you'd have more clean headroom and much less space for tube distortion in the power stage. Hot would mean less tube life and earlier breakup.

Where does it come in that having the right setting will give you a 'tighter' sound?

 

[STRATDELUXER97]

Re: Bias and tone

Pretty simple really....
The more current you pump through your output tubes,the ballsier the tone and with more output and less headroom....

Less current....less output,more headroom,and if you go too low,the amp acts anemic and thin overall.....There's a large margin on the bias adjustments and you'd have to experiment in a range of say 20 to 40 milliamps...I run mine up the middle....Usually around 30 to 34 on my BF Pro Reverb and around 36 to 40 om my 50 watt Marshall...This is done via the 1 ohm cathode resistors I have on my output tubes..

 

[aleclee]

Re: Bias and tone

Pretty simple really....
The more current you pump through your output tubes,the ballsier the tone and with more output and less headroom....

Pretty simple but overly simple IMO.

Lately I've been ranting about how a lot of people bias their amps to 70% of max dissipation without actually listening to the amp. I'd compare that to setting one's neck relief to .009" without actually playing the guitar. It's a reasonable setting but there's a good chance it's not optimal for your playing.

I much prefer the approach of adjusting the bias to where it sounds good and then checking just to make sure it's not over 70%. It's more like the iterative process of adjusting neck relief and playing to make sure it works for you. It also strikes a balance between tone and tube life. Why bias the tubes hotter than necessary to get your tone?

 

[drew_half_empty]

Re: Bias and tone

I got a question about that though

say you bias it cold, then crank the crap out of it

would that have the same effect as biasing it warm & playing at lesser volumes?

 

[aleclee]

Re: Bias and tone

I got a question about that though

say you bias it cold, then crank the crap out of it

would that have the same effect as biasing it warm & playing at lesser volumes?

nope. Think of bias as running a carburetor too rich or too lean and cranking the amp like revving the engine.

 

[STRATDELUXER97]

Re: Bias and tone

Pretty simple but overly simple IMO.

Lately I've been ranting about how a lot of people bias their amps to 70% of max dissipation without actually listening to the amp. I'd compare that to setting one's neck relief to .009" without actually playing the guitar. It's a reasonable setting but there's a good chance it's not optimal for your playing.

I much prefer the approach of adjusting the bias to where it sounds good and then checking just to make sure it's not over 70%. It's more like the iterative process of adjusting neck relief and playing to make sure it works for you. It also strikes a balance between tone and tube life. Why bias the tubes hotter than necessary to get your tone?

See I don't really like putting numbers out there for people....I'm playing through the same tube amps for many years and I know what works for me.I also know what tubes I Like in each of my amps and what doesn't work or sound right...

I have the formula written down and I think I mentioned it somewhere on the posts about figuring out the tube's dissipation and how it relates to an amp's plate voltages....

Everytime I check bias or replace tubes and rebias my amps,I then check my plate voltages and I keep track of the -bias voltage....

I always think of the bias settings as the idle speed setting of your engine...When you step on the pedal you accelerate,but when you let go,you go back to the idle speed setting every time...Your carburetor rich/lean scenario is great also.... :wink: :dance:

Some great info on the postings from all...

 

[aleclee]

Re: Bias and tone

SD97,

I think we're saying similar things but I perhaps read too much into your generalization. You know what works for you and your amps because you tried things rather than turning the knob 'til the meter read 70% and patting yourself on the back becauase your tubes were running nice and warm.

I have a buddy who swears by biasing his EL34 Rivera at 30-32ma. That's only about 50-55% of max dissipation. He sounds great and his tubes will last a heckuvalot longer. I'm not saying that he'd sound worse at 70% but he arguably wouldn't sound any better and would certainly be wasting tube life.

 

[drew_half_empty]

Re: Bias and tone

nope. Think of bias as running a carburetor too rich or too lean and cranking the amp like revving the engine.

good analogy, you know me too well

 

[STRATDELUXER97]

Re: Bias and tone

SD97,

I think we're saying similar things but I perhaps read too much into your generalization. You know what works for you and your amps because you tried things rather than turning the knob 'til the meter read 70% and patting yourself on the back becauase your tubes were running nice and warm.

I have a buddy who swears by biasing his EL34 Rivera at 30-32ma. That's only about 50-55% of max dissipation. He sounds great and his tubes will last a heckuvalot longer. I'm not saying that he'd sound worse at 70% but he arguably wouldn't sound any better and would certainly be wasting tube life.

Check this out...I've done tests during different times of the day regarding wall voltages...One thing we've left out of the equation is wall voltage....I've seen my wall voltages change as much as 3 ac volts or more...That's a pretty big increase in what our amp's see when the voltages rise...

I normally set my 50 watt old Marshall for 36-40 millivolts and I don't feel that these settings in my case(are at all cold)....I also know from experience that my overall tone doesn't change much above these settings and I do wear out tubes faster....I have several tube amps and non-tube amps though,so by rotating my gear around,the tube replacement issues in one amp don't exist...

In fact,lately I'm only using either my Vox Valvetronix head or my Fender Cyber Twin...I'm way beyond the tube amp only mentality these days and I'll now play through whatever gets me a good tone... :dance:

I have tryed the method of having a meter all set up within my amp and I'd adjust the bias and listen...I also tryed the same tests without a meter...I found an area of adjustment that worked for me within a small range...Now whenever I retube and rebias,I'll just go ahead and set my amp(s) up to an actual reading that was written down years ago during that learning process..

As I said,I know what works for me,I have great ears,and I hate telling someone to just set ther amp at "35 millivolts".... :newangel: :smack:

 

[aleclee]

Re: Bias and tone

Check this out...I've done tests during different times of the day regarding wall voltages...One thing we've left out of the equation is wall voltage....I've seen my wall voltages change as much as 3 ac volts or more...That's a pretty big increase in what our amp's see when the voltages rise...

Yeah, and it gets worse when you start playing out in places with dodgy electrics.

3VAC isn't so bad, Even my Furman voltage regulator (highly recommended) only guarantees that degree of variance.

 

[STRATDELUXER97]

Re: Bias and tone

Yeah, and it gets worse when you start playing out in places with dodgy electrics.

3VAC isn't so bad, Even my Furman voltage regulator (highly recommended) only guarantees that degree of variance.

Again there's a formula...3 volts does make a difference in the way an amp operates...I think I read more about this in one of my Gerald Weber books?

"Yeah, and it gets worse when you start playing out in places with dodgy electrics. "

LOL....Been there,done that... :laugh2:

 

[Quencho092]

Re: Bias and tone

Ah, good to know. I biased my bandmaster when i first changed the tubes and set it at 31 mA. I'm going to have to bias my twin RI (coming soon), factory settings are typically ice cold (19-25mA).

 

[Zerberus]

Re: Bias and tone

....

"Yeah, and it gets worse when you start playing out in places with dodgy electrics. "

LOL....Been there,done that... :laugh2:

Ditto, but at least tube amps will still work, albeit not perfectly, under conditions where some SS equip simply refuses

 

[Quencho092]

Re: Bias and tone

you can bias transistors right?

 

[STRATDELUXER97]

Re: Bias and tone

you can bias transistors right?

A given transistor is picked to work within certain ranges within a circuit...They are ss devices and non-adjustable..The device itself is non-adjustable actually...

 

[Gearjoneser]

Re: Bias and tone

There's a lot of guys who do it by ear, within parameters of numbers like 6L6 (31-34mA) and EL-34's (36-40mA). The bottom line is that you want the amp to sound as punchy and bold as possible. It's usually pretty obvious. I lay my guitar on the ground, with the chassis on it's side, leaning against the cab. With my left hand I strum the D and G strings, and with my right hand, I make slight adjustments on the minipot. When the amp sounds it's best, I leave it, and make sure the numbers on my Volt/Amp meter are pretty close to the right numbers.