...afraid to ask!

[old_coot88]

Again, this is why the grid needs to be biased at the midway/ idling/ 50% point, to prevent clipping and minimize distortion. So the tube can handle the highest signal amplitude consistent with good linearity (as in an audio stage). The raucious sound of 'heavy metal' music was spawned from deliberately running tube stages into clipping.

[Chris K]

Originally Posted by old_coot88

Again, this is why the grid needs to be biased at the midway/ idling/ 50% point, to prevent clipping and minimize distortion. So the tube can handle the highest signal amplitude consistent with good linearity (as in an audio stage). The raucious sound of 'heavy metal' music was spawned from deliberately running tube stages into clipping.

OK...since I'm a bioscience guy who needs explanations at the amino acid level, I'm trying to reduce what's going on with the grid to a physical state. Biased at 0%, a tube grid is a grid or screen of fine wires with no voltage, and hence, no free electrons present on it. A tube biased at 100% has a screen saturated with the maximum number of electrons present it can retain. I think I understand the cathode to plate flow part that's regulated by biasing of the grid but now, I'm looking to better understand the grid itself and what's going on with it when the tube is biased.

[old_tv_nut]

Originally Posted by Chris K

OK...since I'm a bioscience guy who needs explanations at the amino acid level, I'm trying to reduce what's going on with the grid to a physical state. Biased at 0%, a tube grid is a grid or screen of fine wires with no voltage, and hence, no free electrons present on it. A tube biased at 100% has a screen saturated with the maximum number of electrons present it can retain. I think I understand the cathode to plate flow part that's regulated by biasing of the grid but now, I'm looking to better understand the grid itself and what's going on with it when the tube is biased.

In most cases, the control grid is biased negative with respect to the cathode. "Free electrons" is a poor decriptor of what's going on. All metals have "free" electrons. A better term is a negative charge consisting of excess electrons.
Also, you would say "the tube is biased" at a certain current, not "the grid is biased at a certain percent."

In the case of a linear "class A" amplifier, the maximum possible current (which you called 100%) is determined by the power supply voltage and load resistor when the voltage across the tube (plate with respect to cathode) is zero. Then, the entire power supply voltage is applied to the load resistor with zero volts appearing across the tube. This may be a hypothetical case, because it may be impossible for the tube to draw that much current.

In general, a class A amplifier stage will be biased at a point where the quiescent bias current is halfway between zero and the maximum possible, so there is an equal range above and below the bias point for the output signal to vary up and down.

[zeno]

If someone posted posted a simple tube type audio amp schematic
tht would help the lesson.

BTW if you look at tube spec sheets there is a "cut-off" voltage listed
This is the point at which the tube turns off. If you go above that point
the tube starts to conduct.

Zeno

[old_coot88]

One can think of 'charge' this way: an excess of surface electrons is a negative (-) charge, while a dearth of surface electrons is a positive (+) charge.

A tube's cathode expresses a negative charge, while the anode(plate) has a positive charge. Thus electrons boiled off a hot cathode are attracted strongly to the anode and accelerate toward it, as though the anode were a sump or 'sink' for the electrons.

This gal gives a pretty decent mini-tutorial on the history and development of the triode. https://www.youtube.com/watch?v=0Smj2nHo9zA

[Chris K]

OMG...I think I'm starting to understand this!

[old_coot88]

If you happened to catch her follow-on vid about regeneration https://www.youtube.com/watch?v=DRDajFYCrt0 at 7:42 she incorrectly shows the PHYSICAL location of the "Wing Circuit" coil (although it's correct circuit-wise). It is PHYSICALLY located either next to, or wound directly over the antenna coil's secondary. That's where the crucial feedback coupling occurs. Hence it's traditionally been called the 'Tickler Coil'.

[Chris K]

I did not but it was very interesting to see that a streak on the inside of one of the original Edison light bulbs was the start of it all.

[Alex KL-1]

Originally Posted by old_coot88

That's what I assumed - that a floating grid would eventually bias itself off. Maybe there's some particular I was missin'.

If memory serves me well, I think is something about the geometric distances and metal work funcion, so is limited to some potential, insufficient to cut-off most tubes, especially power tubes (= meltdown).