1. If bias servo is under compensated when output power high then suddenly low, the bias will lower and can not immediately back to the normal value. Amplifier will distort until the bias back to the normal value.
2. Distortion will rise a bit, but harmonic profile will change. Choose for the best sound subjectively.
What amp? What "spec"?
tl;dr - yes. In some cases, I've seen measurably lower THD along with a change in the harmonic distortion profiles. Sometimes that has a pleasing audible effect (to me).
You post a lot of questions as independent threads, which is cool. In this case, perhaps consider asking the question in the thread(s) for the amp(s) you're most considering. You may get more meaningful answers.
You can check one of 6L6's guides (I wish I could remember which, but you can find it easily) for one clear example with pictures as he varies the bias and chooses the point that he likes best.
tl;dr - yes. In some cases, I've seen measurably lower THD along with a change in the harmonic distortion profiles. Sometimes that has a pleasing audible effect (to me).
You post a lot of questions as independent threads, which is cool. In this case, perhaps consider asking the question in the thread(s) for the amp(s) you're most considering. You may get more meaningful answers.
You can check one of 6L6's guides (I wish I could remember which, but you can find it easily) for one clear example with pictures as he varies the bias and chooses the point that he likes best.
some questions are good (and answered properly) when asked in broad context
some questions are best answered when asked in firm/narrower context
I like most questions of type "is that amp better than that another amp?"
after some time ( even if I'm lost case with both short and long memory when social context is in case), I'm getting impression that Greedy Boyz who are asking that sort of question repeatedly - much more enjoy asking questions than actually building anything
no complain from my side, just stating that they are missing enormous joy of making things with own hands and brain .......
and - yes - I'm taking in account that some of us are on tight budget when audio thingies are in question ..... but there are plenty of projects possible with peanut money investment ........ and involving even greater level of creativity - how to spend less money....... most important thing is that constipation of my wallet doesn't need to constipate my brain
some questions are best answered when asked in firm/narrower context
I like most questions of type "is that amp better than that another amp?"
after some time ( even if I'm lost case with both short and long memory when social context is in case), I'm getting impression that Greedy Boyz who are asking that sort of question repeatedly - much more enjoy asking questions than actually building anything
no complain from my side, just stating that they are missing enormous joy of making things with own hands and brain .......
and - yes - I'm taking in account that some of us are on tight budget when audio thingies are in question ..... but there are plenty of projects possible with peanut money investment ........ and involving even greater level of creativity - how to spend less money....... most important thing is that constipation of my wallet doesn't need to constipate my brain
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It is likely that all the first watt style amps sound better with more bias than stock.
It is unlikely you have the heatsink available to bias them much higher than stock.
So most live with the amps at factory bias levels. Bias is one leg of the 3 sided triangle of heat/rail voltage/bias. All amplifiers are a balancing act of these 3 points. If you can compensate for heat with a larger chassis you can have more bias. If you lower the rail voltage you can have more bias at the expense of output wattage. Its a balancing act.
I have a 5U chassis so my F5 runs 1.7A bias and two pairs of mosfets vs the stock 1.4A and a single pair of mosfets. Does it sound better? Yes, I think so.
I have also used a basically stock F5 w/2A of bias. Yes, it sounds better.
It will depend on your speakers and listening habits but in general, more bias almost always sounds better. Fuller, more depth, more 3D.
In this case I did kinda want a broader set of answers, in case someone was like "Well, in *this* case, setting a high bias does have a big effect, but in this *other* case it doesn't".
I guess I'll just have to do some experiments with my amp once I get setup to take proper measurements and see what I can see.
Sorry for asking so many questions, I do learn a lot by doing so, which leads into my future projects! But, I will ask fewer questions from now on.
I guess I'll just have to do some experiments with my amp once I get setup to take proper measurements and see what I can see.
Sorry for asking so many questions, I do learn a lot by doing so, which leads into my future projects! But, I will ask fewer questions from now on.
The power supply should be designed to the higher current. Usually ripple noise gets higher and can be audible in low passages in the music.......or in idle mode.....which I don't like.
If you don't get lower distortion what is the benefit?
I think change in bias should be backed up by measurements to ensure the change was to the better.....you may just get more 50/100 Hz noise (or 60/120).
If you don't get lower distortion what is the benefit?
I think change in bias should be backed up by measurements to ensure the change was to the better.....you may just get more 50/100 Hz noise (or 60/120).
I got to about "X*?@!" last night when experimenting. Then my 3A fuse went
I suppose I could up the fuses 
It is getting cold here in Sacramento... 
I got to about "X*?@!" last night when experimenting. Then my 3A fuse went
LOL what is it, 65deg?
About that, I think I read ~62 on the external heatsinks, and ~72 on the heatsinks for Q3/Q4 on the front end.
When I took the fuse holder out to change the fuse it was too hot to handle