Bias settings for common power tubes

[TIMBO]

Hi guys, Sometime ago a list of bias settings was produced by someone on the forum.
Does anyone know where to find it?
Thanks

[Dave]

I use the Weber Bias Calculator.


Dave

[tdvt]

I am thinking it was these?

I don't recall who made/posted them either, but seems I downloaded the whole set when I saw them.

[Latole]

I use the Weber Bias Calculator.


Dave

It does the job for all tubes, no need more

[TIMBO]

Thanks for that
 

[pdf64]

I suppose they’re helpful to folk with a mental block in regard of basic arithmetic, but all of them seem to use inconsistent values for the anode dissipation limit of one or more valve types.
And they promulgate the perception that class of operation is determined by dissipation %, eg class AB is 70%, class A is 90%. So act to muddle people’s understanding of how circuits work and prevent them progressing.

[Dave]

Math is fascinating. So is astrophysics. Unfortunately, my education falls more in the humanities neighborhood. The calculator has worked well for me, so I use it.


Dave

[ac427v]

Somewhere along the way I got the impression that the impedance of the output transformer also affected ideal bias. I never see this mentioned in charts or on-line calculators.

[pdf64]

Somewhere along the way I got the impression that the impedance of the output transformer also affected ideal bias. I never see this mentioned in charts or on-line calculators.

That’s going into the weeds rather.
To a large extent, idle dissipation is only relevant to idle conditions, so load impedance is irrelevant to that.

Additionally, ‘ideal bias’ may be something of a nebulous concept, perhaps exists only in the (golden) ear of some discerning listeners. Any properly designed amp accommodate a range of settings.

An amp’s designer should be aware of all the various aspects of its operating point and various considerations and constraints.  All that data seems well outside the scope of generic tables / calculators. They’re already on a significant overstretch by equating some particular idle dissipation to a particular class of operation.

[acheld]

the impedance of the output transformer also affected ideal bias.

It does!   The "reflected" load has a direct relationship with plate current.

To me, biasing is all about a compromise between a hot tube, and tube life. It's been said that a good compromise between sound quality and tube life occurs when you bias (fixed, of course) at 70% of max Pdiss.

I'm not so sure that is true -- I get great tone from my amps down in the 50% range most of the time, though I normally bias around 60-65% -- and my tubes last a very long time.  When you bias very low, the amp sounds lifeless to me.   When biased high (say 80%), the amp sounds fine -- though some folks can hear difference and like the tone at that level (my old ears don't hear this!) -- but there would be an expected reduction in tube longevity. What the exact relationship is between bias level and longevity is, I don't know.   I bet the tube manufacturers do know, however.

Reminds me of my first experiences with Blues Juniors back in the day.  They were all biased very hot from the factory, and the EL84s would burn up in a matter of months.   When we reduced the bias (via BillM mods), the amps sounded the same, but the tubes would last forever.   

[pdf64]

the impedance of the output transformer also affected ideal bias.

It does!   The "reflected" load has a direct relationship with plate current.
 …

Under dynamic conditions, yes, but generic tables / calculators are restricted to data and dissipation at idle

[tubeswell]

Aiken has a good article


https://www.aikenamps.com/the-last-word-on-biasing