Anyone willing to educate me on what's actually flowing through these wires?

I'm trying to figure this all out.

Within the same wires/lines in my amp, there's the signal (which is AC), B+ (which is DC), electrons (which is DC too but flowing the opposite direction of B+), and what else am I missing. Do these three ever get mixed up because they are sharing the same wire? Is AC alternating + and -? If that's the case, wouldn't it disrupt the flow of B+ and Electrons?

It's killing me to look at a schematic and not understand what's going on.

(One day, I am going to look back and be embarrassed for asking these questions. But at the same time, I suppose, it would be my proudest moment because I would then have understanding of it all.)

Thanks.

My suggestion is to buy yourself a basic electronics text book. There are those of us (such as myself) who have gone through great effort and expense to educate ourselves about what exactly is going on, and I don't think a simple forum post can begin to convey what you seek to understand.

At least search online for some electronics tutorials. There's even good vacuum tube tutorials out there as well.

...but I'll start explaining anyway. The flow of electrons is electric current. The guitar signal is an ac current---or an alternating flow of electrons. By 50/50 chance, the convention for positive voltage potential and the charge of an electron was decided in what some may call the "wrong way". This just means that what we conventionally call positive current is actually electrons flowing the other way. Don't worry about it.

Okay, have you ever seen a little table-top wave tank? Or think of just a wave in the ocean---not a breaking wave, but a wave coming in from sea before it gets to the shore to break. The sea level is like dc, while the wave on top is ac. The ac rides on top of the dc. The dc level gives the ac something to ride on top of. If you take away the dc, the wave ain't gonna make it to shore.

To really understand more specifically what's going on with your amp circuitry and why takes a bit more learning. You can start by checking out Ohm's law.

It takes a long time before this is totally intuitive...but this might help in visualizing the process:

First, think of a power supply as an electron suction pump. Electrons are drawn toward the B+ terminal. They come from ground, which is a giant pool of electrons.

A power supply does not shoot out electrons, it sucks them in.


So, imagining this as plumbing instead of electronics:

Voltage is like water pressure. Current is like water flow. B+ terminal is a suction pump.

At a zero AC signal state, the power supply is sucking in electrons and at each point of the circuit there is a certain pressure and flow (voltage and current), set by the DC bias on the tubes.

A tube is like a valve (hence the British term) and the DC grid bias voltage sets the normal or standby flow.

When you apply an AC signal to the grid, it is like grabbing the handle on a spigot and wiggling it back and forth, changing the current (water flow). AC is superimposed on the DC control voltage.

Between the tube/valve and the power supply there is a load resistor. The resistance doesn't change but the current through it does due to the tube. As the current goes up, more voltage is dropped across the resistor, less current = less voltage drop.

So the way a tube amplifies, is a small AC voltage applied to the grid swings the output current back and forth. This current goes through a resistor, creating a swinging voltage drop which is much larger than the AC signal applied to the grid. Voila, amplification!

Note that a positive change at the grid creates a negative change at the other side of the resistor...each tube stage inverts the signal. A positive going signal means more current flow and hence more voltage drop across the resistor, ie. more negative voltage.

You can then take that amplified signal and run it through another tube and load resistor to enlarge the AC voltage swing even more.

After two 12AX7 stages, a fraction of a volt input signal can be up in the 20-30V range--enough to overdrive a power tube.

Basically, an amplifier swings variable current through a load resistor and picks a changing voltage (signal) off of the load resistor.

AMPLIFIED AC SIGNAL IS DEVELOPED ACROSS A LOAD RESISTOR, due to varying current flow caused by varying the grid voltage with an input AC signal.

A coupling cap (aka blocking cap) after the load resistor only lets AC signal through and it blocks the DC in the plate circuits so it doesn't mess with the DC grid bias of the next tube.

So, in summary, DC voltages set up the static operating currents of the amp. Applying AC to tube grids changes the current flows and causes big voltage drops across load resistors--way bigger than the input signals.

That is a bit simplified but the basic deal.

In order to visualize what is going on you have to think of electrons flowing from ground, up through the tubes, and into the power supply. Tubes control the rate of flow and a combination of AC and DC voltages are the control mechanism. The change in flow creates voltage drops across resistors and that where amplification occurs.

Make sense?

"A power supply does not shoot out electrons, it sucks them in."

THIS is what took me A LONG TIME to understand. It was a light bulb moment for me a few years ago. Someone explained it this way:

An analogy would be sucking water out of a glass with a straw. Your mouth represents the power supply (B+)...the water represents the electrons...and the straw represents the level of resistance. Sucking stronger on the straw = more voltage. A larger diameter straw = more current flow. Voltage and current have a 1 to 1 ratio in a perfect world...a world of no resistance. I always wondered, "why add resistance to a circuit in the first place?"

BUT, a perfect world doesn't exist because every circuit has some resistance. Take away the resistance (straw), and there is no way a circuit will function. When I understood this fact, it started to make sense.

Good thread!!!! Gronk want more. Hands on/ analogies , then theory I say!!!!!

Here's a good page explaining how tubes themselves work: http://www.john-a-harper.com/tubes201/

Ok, what about dark current then?

Ok, what about dark current then?

Variances in dark current draw are what cause tubes with otherwise identical characteristics to sound wildly different to those with "good" ears. :lol:

- Scott

How rude, guys!!:wink: WELCOME TO THE TDPRI efnikbug!!!!!

Good stuff! I always thought there was magic involved somewhere.

Oop. Double post.

My suggestion is to buy yourself a basic electronics text book. ...I don't think a simple forum post can begin to convey what you seek to understand.


+1 on this.

The subject is pretty involved and to be honest your questions suggest you need to start at the very beginning.

For what it's worth, I started reading kids 'Fun with Electricity' type books when I was 9 or 10 and have read casually about circuits ever since. I am far from an expert, so don't expect it all to become clear at once.

"...An analogy would be sucking water out of a glass with a straw. Your mouth represents the power supply (B+)...the water represents the electrons...and the straw represents the level of resistance. Sucking stronger on the straw = more voltage. A larger diameter straw = more current flow.

...And choking while sucking all that water: blown fuse!

Sorry, could not help myself:lol:

wiring panels.....before going back to University...and it still seems like magic at times! One thing is for sure....I know what 600 volts can do !!:!:
iggy

+1 on this.

The subject is pretty involved and to be honest your questions suggest you need to start at the very beginning.

For what it's worth, I started reading kids 'Fun with Electricity' type books when I was 9 or 10 and have read casually about circuits ever since. I am far from an expert, so don't expect it all to become clear at once.

check hoffmanamps.com

They have a current diagram up there that I found helpful. show's a color coded view of how it all works.

check hoffmanamps.com

They have a current diagram up there that I found helpful. show's a color coded view of how it all works.
I came across it last night, and thought it a coincidence to come across your post this morning.

Thanks, everyone!
http://www.el34world.com/charts/images/currentdiagram1.gif