[Amps] Changing class of operation with BIAS

[Joe Subich, W4TV]

> 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
>   
>