Calculate unknown operating point from known cathode resistor

[Blue Jinn]

I just can't get my head around this one.

I want to change B+ on a circuit.

I know existing B+ and plate resistor. I can draw a load line.

So far so good. Knowing the cathode resistor, how do I figure the existing operating point?

 

[rayma]

I just can't get my head around this one.

I want to change B+ on a circuit.

I know existing B+ and plate resistor. I can draw a load line.

So far so good. Knowing the cathode resistor, how do I figure the existing operating point?

For say 1mA, determine the voltage drop on the cathode resistor. Then plot that grid bias point, at that current, on the graph with the load line.
Repeat for other current values. The intersection of the locus of these points with the load line is the operating point. Cool, huh?

 

[Malcolm Irving]

Have a look on Merlin's webpages:

How to design valve guitar amplifiers

In the section on 'Triode Gain Stage', look at page 13 on 'The Cathode Load Line'.

 

[Blue Jinn]

Ah, thank you folks.

Merlin's chapter does make it easier to visualize too. (I have been advised on numerous occasions to get his book, which is on my todo list...) 🙂