Ahoi,
hab wieder ne Mail bekommen - und ich soll "free feeln" das rumzupassen
hier zitiere ich Roger von Peavey:
"Bias isn't really that critical. Here is some information that might
help, and feel free to pass it on to your friend as well.
When we refer to biasing an amplifier, that generally means we are
setting the idle current for the power tubes.
The idle current is the current present when there is no signal passing
through the tube. It is adjusted by changing the bias voltage, which is
a negative voltage applied to the grid of the tube.
As the bias voltage becomes more negative, the current becomes smaller,
and the tube is said to be biased "colder". As the bias voltage becomes
less negative, the current goes up, and the tube is said to be biased
"hotter".
A Class AB amplifier must be biased within a certain range in order for
the tube to function correctly.
If the bias voltage is set to far negative, a number of things can
happen. The tubes will get very near their cutoff point at crossover,
and crossover distortion can be severe enough to adversely affect the
sound. The output itself can be weak, since less voltage also means less
current flow.
If the voltage is set too far positive, the tube will dissipate more
current than it should. Output goes up, but this will shorten tube life
and can cause premature failure of the tube.
In between those two extremes is a wide range of safe operation. A
power amp can be loud and clean with the bias current set over a range
of values. If we have an amp where 50ma plate current will start to melt
the power tubes, and 5ma all but chokes off the signal, we find that the
amp works well if the tubes draw 17ma, or 22ma, or 15ma, etc. So it
doesn't ultimately matter if a set of tubes is several milliamps hotter
or cooler than another. They will still fall within the range of good
performance.
The reason for the fixed circuit that is used in our current line of
guitar amplifiers is based on our policy of providing quality gear at a
reasonable price. We try to do anything we can on the design end to give
our customers a quality, reliable product that will provide many years
of trouble free use.
Our circuit extends tube life and saves you money, since the tubes can
be user replaced without the added expense of putting it in the shop and
having a tech adjust it every time.
I hope this was helpful!
Regards,
Roger Crimm
Regional Service Manager
Peavey Electronics"
