Tube Bias Chart - FYI

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Ventura

Ventura

Well-known member
Here's a great table of most common tubes. The new JJ KT-88s are absolutely amazing bottles regardless of the price making them seem "run of the mill". Likely some of the finest 88s I've seen and heard. Just FYI.

But anyway - here's a chart for pV and related mA settings.

 

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Are these at 70% plate dissipation? Are these for triode strapped or full pentode power tube designs?

I'm hesitant to go by big charts like this because each amplifier is different in how the power amplifier is designed. It's also important to note that the output transformer primaries impact bias currents as well which change amplifier to amplfier.

I don't recommend people go by this - for reasons mentioned above. Looking at it further, there are some tubes listed that cannot even tolerate 500V or 600V tolerances (100V+ to 200V+ over tolerance).

Old datasheets are always the best way.
 
Looks like Min is Class AB at 50% and Max is Class AB at 70%.

[note: I wouldn't recommend putting 600V on the plates of EL84s :)]
 
V2a":k39mtzzt said:
Looks like Min is Class AB at 50% and Max is Class AB at 70%.

[note: I wouldn't recommend putting 600V on the plates of EL84s :)]
Click to expand...

+1

Hell, it has some 6L6 bottles showing 500V and 600V on the plates capable of being biased up. People would be weary to find out 6L6 bottles aren't rated to handle more than 400V max. That's why the military created 5881's which were a series that could handle a higher B+ rating. They'll burn up quicker than a candle in a power outage.
 
glpg80":2e1y3qav said:
People would be weary to find out 6L6 bottles aren't rated to handle more than 400V max.
Click to expand...

That's funny... And, absolutely false. Maybe "some", can't, but most current production can handle 500V. If this were true, there'd be alot of 6L6-loaded amps pushing 460-490V that are shit out of luck, no?
 
napalmdeath":21x9ajpo said:
glpg80":21x9ajpo said:
People would be weary to find out 6L6 bottles aren't rated to handle more than 400V max.
Click to expand...

That's funny... And, absolutely false. Maybe "some", can't, but most current production can handle 500V. If this were true, there'd be alot of 6L6-loaded amps pushing 460-490V that are shit out of luck, no?
Click to expand...

Absolutely true - dig up the datasheets yourself. Doesn't mean the tubes cannot be run with a higher PV, but that is not what they were rated for. You're confusing intended ratings and absolute max ratings.
 
glpg80":10mwl8z3 said:
napalmdeath":10mwl8z3 said:
glpg80":10mwl8z3 said:
People would be weary to find out 6L6 bottles aren't rated to handle more than 400V max.
Click to expand...

That's funny... And, absolutely false. Maybe "some", can't, but most current production can handle 500V. If this were true, there'd be alot of 6L6-loaded amps pushing 460-490V that are shit out of luck, no?
Click to expand...

Absolutely true - dig up the datasheets yourself. Doesn't mean the tubes cannot be run with a higher PV, but that is not what they were rated for. You're confusing intended ratings and absolute max ratings.
Click to expand...

Aren't you confusing yourself as well? You said "aren't rated", when, in fact, they are rated for 500V, in most cases. You're generalized statement is false.

https://www.amplifiedparts.com/tech-cor ... made-tubes
 
napalmdeath":g1emp9yj said:
glpg80":g1emp9yj said:
napalmdeath":g1emp9yj said:
glpg80":g1emp9yj said:
People would be weary to find out 6L6 bottles aren't rated to handle more than 400V max.
Click to expand...

That's funny... And, absolutely false. Maybe "some", can't, but most current production can handle 500V. If this were true, there'd be alot of 6L6-loaded amps pushing 460-490V that are shit out of luck, no?
Click to expand...

Absolutely true - dig up the datasheets yourself. Doesn't mean the tubes cannot be run with a higher PV, but that is not what they were rated for. You're confusing intended ratings and absolute max ratings.
Click to expand...

Aren't you confusing yourself as well? You said "aren't rated", when, in fact, they are rated for 500V, in most cases. You're generalized statement is false.

https://www.amplifiedparts.com/tech-cor ... made-tubes
Click to expand...

Nope, I am not.

First of all, I said look at the datasheets. Not a website supplier looking for your money.

I also stated the 6L6 series, not the 6L6 GA, GB, or GC, or 5881's for that matter. Based on the chart, it states it can be biased up at 600V in a class A/B amplifier.

datasheet.png


Here's another example. An original RCA datasheet which I've taken the time to screenshot each page and highlight the limit as stated.

datasheet_2.png


Now tell me where I'm wrong such that a 6L6 based tube, as stated within the OP's chart, can be biased to 600V and work as originally intended?

I'll reiterate that tubes these days may be run with a higher PV, but that is not what they were rated for. It will degrade the total lifespan of the tube especially on startup and shutdown sequences, as there is a max heater-cathode tolerance voltage and also a max plate-grid voltage tolerance.
 
glpg80":2k9xil49 said:
Nope, I am not.

First of all, I said look at the datasheets. Not a website supplier looking for your money.

I also stated the 6L6 series, not the 6L6 GA, GB, or GC, or 5881's for that matter. Based on the chart, it states it can be biased up at 600V in a class A/B amplifier.

Here's another example. An original RCA datasheet which I've taken the time to screenshot each page and highlight the limit as stated.

Now tell me where I'm wrong such that a 6L6 based tube, as stated within the OP's chart, can be biased to 600V and work as originally intended?

I'll reiterate that tubes these days may be run with a higher PV, but that is not what they were rated for. It will degrade the total lifespan of the tube especially on startup and shutdown sequences, as there is a max heater-cathode tolerance voltage and also a max plate-grid voltage tolerance.
Click to expand...

glpg80's points are well taken (and accurate). And in an attempt to nip other "debates" in the bud, not all 6V6s are JJ 6V6Ss...
 
napalmdeath":3ity28qa said:
glpg80":3ity28qa said:
napalmdeath":3ity28qa said:
glpg80":3ity28qa said:
People would be weary to find out 6L6 bottles aren't rated to handle more than 400V max.
Click to expand...

That's funny... And, absolutely false. Maybe "some", can't, but most current production can handle 500V. If this were true, there'd be alot of 6L6-loaded amps pushing 460-490V that are shit out of luck, no?
Click to expand...

Absolutely true - dig up the datasheets yourself. Doesn't mean the tubes cannot be run with a higher PV, but that is not what they were rated for. You're confusing intended ratings and absolute max ratings.
Click to expand...

Aren't you confusing yourself as well? You said "aren't rated", when, in fact, they are rated for 500V, in most cases. You're generalized statement is false.

https://www.amplifiedparts.com/tech-cor ... made-tubes
Click to expand...
Hey Napalm: He's talking about the old style 25watt 6L6 & 6L6G etc., NOT the typical 30 watt 6L6GC that most of us are using these days.

So you're both right :2thumbsup: :cheers2:

The general idea that glpg80 and others are getting at is, there are parts of that chart for certain tubes that should have been left blank, and I would agree.
 
Having pointed out that some parts of the chart are problematic, particularly for those who might confuse tubes, I also want to note that I downloaded and saved the chart. Very handy! Thanks for posting, Ventura!
 
fusedbrain":2mgb2mbi said:
napalmdeath":2mgb2mbi said:
glpg80":2mgb2mbi said:
napalmdeath":2mgb2mbi said:
glpg80":2mgb2mbi said:
People would be weary to find out 6L6 bottles aren't rated to handle more than 400V max.
Click to expand...

That's funny... And, absolutely false. Maybe "some", can't, but most current production can handle 500V. If this were true, there'd be alot of 6L6-loaded amps pushing 460-490V that are shit out of luck, no?
Click to expand...

Absolutely true - dig up the datasheets yourself. Doesn't mean the tubes cannot be run with a higher PV, but that is not what they were rated for. You're confusing intended ratings and absolute max ratings.
Click to expand...

Aren't you confusing yourself as well? You said "aren't rated", when, in fact, they are rated for 500V, in most cases. You're generalized statement is false.

https://www.amplifiedparts.com/tech-cor ... made-tubes
Click to expand...
Hey Napalm: He's talking about the old style 25watt 6L6 & 6L6G etc., NOT the typical 30 watt 6L6GC that most of us are using these days.

So you're both right :2thumbsup: :cheers2:

The general idea that glpg80 and others are getting at is, there are parts of that chart for certain tubes that should have been left blank, and I would agree.
Click to expand...

I agree. There's certainly parts of the chart that don't apply, and out of whack. I would never suggest running 6L6's at 600v and dont know many amps that require it. Many run in the 460-480 range.

I wouldn't use that chart at all. Use a bias probe and a calculator, and do it right.
 
Just measure plate-to-cathode voltage with a meter
(Tube dissipation in watts * desired dissipation % / Vp) * 1,000 = bias
 
My only issue with the chart (which is handy btw) is that all the bias values listed are calculated at 50% of max plate dissipation. Most everyone I know (including the cautious builders) sets and calculates it at 60% of the max... sometimes 70% depending on how it sounds, feels, responds. 50% is really on the low/cold side. It works fine, and is safe, but not sure if it sounds good, depending on which power tubes in which amps.

Pa Max (Max Plate/Screen Dissipation)
-------------------------------------------------------- X .60 X 1000 = Bias setting in milliamps (mA)
Plate Voltage (should be a number from 400-500V for most amps)

You can substitute the .60 value with .70 depending on how "hot" (how much current passing thru the tubes) you want to run the tubes in the above formula. Many times too hot a setting will too get mushy at loud volumes, but sound fuller/more saturated at low volumes... so experiment.
 
napalmdeath":3t4pm339 said:
I agree. There's certainly parts of the chart that don't apply, and out of whack. I would never suggest running 6L6's at 600v and dont know many amps that require it. Many run in the 460-480 range.

I wouldn't use that chart at all. Use a bias probe and a calculator, and do it right.
Click to expand...
I'll go one further and add use your ears. For me, the calculator gives me the max dissipation I should set it at and then I set it as cold as I can and still get the tone. And that is almost always way, way colder than 70%. Usually closer to 60% but it varies quite a bit.
 
V2a":ny65o7cc said:
Having pointed out that some parts of the chart are problematic, particularly for those who might confuse tubes, I also want to note that I downloaded and saved the chart. Very handy! Thanks for posting, Ventura!
Click to expand...
Pleasure - it's just a rough guideline.

Couple disclaimers - ALWAYS check the individual tubes' spec sheets for tolerances and thresholds; know your amp and its drift; understand your application (are you a "goes to a 11" kinda guy or just a moderate "noon and under" player?), etc.

Another handy little website is:
https://robrobinette.com/Tube_Bias_Calculator.htm

Just throwing some stuff out there I've found interesting... No flamesuits needed.
Play safe Folks, rock hard, life is loud :rock: :rock: :rock: :rock: :rock: :rock:

Peace :thumbsup:
 
SpiderWars":3tszivo2 said:
napalmdeath":3tszivo2 said:
I agree. There's certainly parts of the chart that don't apply, and out of whack. I would never suggest running 6L6's at 600v and dont know many amps that require it. Many run in the 460-480 range.

I wouldn't use that chart at all. Use a bias probe and a calculator, and do it right.
Click to expand...
I'll go one further and add use your ears. For me, the calculator gives me the max dissipation I should set it at and then I set it as cold as I can and still get the tone. And that is almost always way, way colder than 70%. Usually closer to 60% but it varies quite a bit.
Click to expand...

Me too. If 36mA is 70%, I'll likely go 34-ish. I don't always find 70% desirable, and with amps these days relying mostly on preamp gain, a little colder tends to work better for cleaner power/headroom, with high gain monsters, especially.
 
napalmdeath":44kyc8tn said:
SpiderWars":44kyc8tn said:
napalmdeath":44kyc8tn said:
I agree. There's certainly parts of the chart that don't apply, and out of whack. I would never suggest running 6L6's at 600v and dont know many amps that require it. Many run in the 460-480 range.

I wouldn't use that chart at all. Use a bias probe and a calculator, and do it right.
Click to expand...
I'll go one further and add use your ears. For me, the calculator gives me the max dissipation I should set it at and then I set it as cold as I can and still get the tone. And that is almost always way, way colder than 70%. Usually closer to 60% but it varies quite a bit.
Click to expand...

Me too. If 36mA is 70%, I'll likely go 34-ish. I don't always find 70% desirable, and with amps these days relying mostly on preamp gain, a little colder tends to work better for cleaner power/headroom, with high gain monsters, especially.
Click to expand...
100% - gives the amp teeth and percussiveness :yes:
 
Ventura":1zswxtir said:
100% - gives the amp teeth and percussiveness :yes:
Click to expand...

... and will cook your tubes like a potato in a microwave... fast. :yes:

Also anything over 70% usually sounds too mushy/saturated/in-articulate at loud volumes. YMMV.
 
Wizard of Ozz":1v228vrh said:
Ventura":1v228vrh said:
100% - gives the amp teeth and percussiveness :yes:
Click to expand...

... and will cook your tubes like a potato in a microwave... fast. :yes:

Also anything over 70% usually sounds too mushy/saturated/in-articulate at loud volumes. YMMV.
Click to expand...
Heh Heh... pretty sure he meant that he agrees 100% about biasing high gain amps a little colder.
I don't think the V-man is suggesting 100% plate dissipation :lol: :LOL:
 
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