Fender Bassman 100 Head Silverface 1974 - Blows Fuse

[tubeswell]

...or even better a vertical scale, where you can visualize the -40V is a higher voltage than -80V.

Except, that in relation to 0, -80 is more charged than -40 (albeit more negatively charged)

[Leo_Gnardo]

Except, that in relation to 0, -80 is more charged than -40 (albeit more negatively charged)

Dare we introduce the mathematical concept of "absolute value?" More is more, in either direction.

[tubeswell]

Dare we introduce the mathematical concept of "absolute value?" More is more, in either direction.

Indeed. The term ‘more negatively’ can be relatively written as “more ‘negatively’ ”
😀

[Enzo]

Higher on that vertical scale still doesn't mean higher potential. After all a -200 volt charge will shock you more than a -2 volt charge. We get into constructs like "reduce the voltage from -2 to -200." That might make sense in grammar, but not really in electronics.

[Helmholtz]

Except, that in relation to 0, -80 is more charged than -40 (albeit more negatively charged)

Charge and voltage are different things. Charge is defined as capacitance times the voltage difference between two terminals. A charge of a single (voltage) point makes no sense without reference.

[tubeswell]

Charge and voltage are different things. Charge is defined as capacitance times the voltage difference between two terminals. A charge of a single (voltage) point makes no sense without reference.

Indeed they are. Nevertheless, a more negative voltage presents a potential energy that is more negatively charged than a less-negative voltage (with respect to a chosen voltage reference point)

After all, voltage is potential energy difference per unit charge. V= E/Q

[Helmholtz]

Higher on that vertical scale still doesn't mean higher potential.

It does.

After all a -200 volt charge will shock you more than a -2 volt charge. We get into constructs like "reduce the voltage from -2 to -200."

You are mixing up magnitude of voltage difference with voltages.

[Helmholtz]

Indeed they are. Nevertheless, a more negative voltage presents a potential energy that is more negatively charged than a less-negative voltage (with respect to a chosen voltage reference point)

After all, voltage is potential energy difference per unit charge. V= E/Q

A more negative voltage is a lower voltage, corresponds to al lower potential and means a lower potential energy for a positive unit charge.

with respect to a chosen voltage reference point

Exactly. And the reference potential is not necessarily 0V. As said, charge depends on voltage difference.

[tubeswell]

A more negative voltage is a lower voltage, corresponds to al lower potential and means a lower potential energy for a positive unit charge.



Exactly. And the reference potential is not necessarily 0V. As said, charge depends on voltage difference.

You are taking parts of my explanation and separating them in order to construct a false argument.

‘More negative voltage’ can only be understood in relation to a chosen reference point, and I have made this point several times.

In the context of the adopted reference point, a more-negative voltage presents a point of greater charge than a less-negative voltage (setting ‘positive voltage’ aside). What Enzo already said: -200v will shock you more than -20v.

[Enzo]

But indeed the reference point for ALL discussions of amplifier bias is with respect to ground as the zero point, unless specially noted beforehand. No one is proposing a single point, referenceless voltage.

A charged cap is a good example, charge it to 80v and it has more voltage stored than if you charge it to 40 volts. And it doesn't matter which end you use as a reference, it still has an 80v charge. And that still is more than it would be at 40v.


Again, I think it confuses far more people to say we reduced or lowered. -2v to -200v than it makes sense to.

Or imagine the other direction. I have a 9v battery wired as a negative supply. Should I say that as my battery wears out, my voltage increases?

[eschertron]

I don't really think that my body will care whether 1 Coulomb of electrons are entering or leaving my fingers when I stick them into a high voltage circuit. Either way, it's a lethal shock!

So while, in absolute value, -200vdc is less than 0vdc, there's still a much greater potential. Can we agree to let the OP understand that -80vdc bias on the control grid has a greater potential than -40vdc to resist the power tube's conduction?

edit: I see that we're piling on! Sorry.

[Helmholtz]

What Enzo already said: -200v will shock you more than -20v.

Sure, but what matters regarding shock is the voltage difference between the two points you touch and not the difference to 0V. If you touch -200V on one side and -200V on the other, you won't get shocked. So this example doesn't prove anything.

[Enzo]

Sorry if we are piling on. I have respect for Helmholtz and his technical knowledge and awareness. I think we are establishing a consensus, rather than piling on. in honesty, I think Helm is making a pedantic argument for a semantic nuance. In terms of practical electronics, I don;t think it is valid.

And this debate is unfolding as it does every time it starts.

[Helmholtz]

So while, in absolute value, -200vdc is less than 0vdc, there's still a much greater potential. Can we agree to let the OP understand that -80vdc bias on the control grid has a greater potential than -40vdc to resist the power tube's conduction?

Sorry, if this discussion gets confusing to some.

A bias of -80V produces a stronger electron repelling field between cathode and grid than -40V and thus causes (strongly) reduced plate and screen currents.

[Enzo]

That is true, and independent from whether we label that a reduction or increase in the voltage. I don't think there is any disagreement over what that voltage change does to the tube currents. I think the only thing we are going back and forth over is how to label the voltage change.