If you increase plate voltage alone, which results in a higher plate
current with no signal applied, are you indeed changing the bias? Yes
or no.
No. You are changing the operating point (operating conditions) but
not the bias (unless the bias is generated by a voltage drop across
a cathode resistor).
In general, in a triode increasing late voltage will increase the
idle current, increase the conduction angle of the tube and move the
operating point more toward class A (class being defined by conduction
angle).
On the other hand, in a triode, increasing the grid bias will decrease
the idle current, decrease the conduction angle and move the operating
point closer to cut-off (class B or class C).
73,
... Joe, W4TV
On 2019-10-31 6:54 PM, Mark Bitterlich wrote:
It seems that my original question generated some interest, and I have
received several private replies. A majority of them espouse some
interesting viewpoints that make me question what I thought I knew.
So I am asking this amplifier theory question again.
BIAS is defined as the difference in potential between the cathode and the
control grid.
In a zero signal condition, BIAS current is a result of the difference
described above.
Thus BIAS can be described by the difference in voltage between control grid
and cathode or as an indication of plate current with no signal applied.
Question:
If you increase plate voltage alone, which results in a higher plate current
with no signal applied, are you indeed changing the bias? Yes or no.
Thanks,
Mark
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