coupling gain stages?

[flemingmras]

Thank you, that makes so much sense. But when your filter cap is fully charged is the negative terminal showing zero volts or -450?

Again...it's all relative. Relative to ground you'll see zero because the negative terminal is grounded. But relative to the positive side of the filter cap, you'll see -450V. This assumes that your filter cap is charged to 450V of course.

[noworrybeefcurry]

Thats what ive been trying to get my head around; say i had a tap from the negative leg of that cap to another circuit, what would the voltage be on that tap?

[noworrybeefcurry]

Back to the original question, why are the largest filter caps in your power supply only fed voltage and then grounded with no other taps?

[flemingmras]

Thats what ive been trying to get my head around; say i had a tap from the negative leg of that cap to another circuit, what would the voltage be on that tap?

It would be nothing because the filter cap isn't part of that circuit or connected to that circuit's "zero reference".

Recall back to when I stated that your volt meter is your "electrical measuring tape". When you measure with a measuring tape, your measurements are relative to a zero...and that "zero" is wherever zero is on the measuring tape.

It's the same with voltage. Your "zero" is wherever the black lead of your meter is connected to in the circuit.

So...if you reference your "zero probe" (i.e. the black probe) to the negative side of the cap and you connect the red lead of your meter to the negative side of the cap to take a measurement, you've basically just shorted across the meter, in which you have no charge differential because you have both the meter leads connected to the same wire (i.e. the negative side of the filter cap).

It would be the same as connecting your "zero probe" to ground, then taking a measurement off the negative side of your filter cap with the red probe. Since the negative side of the filter cap is ALSO connected to ground (thereby making ground your "zero"), you've just connected both of your meter leads to your "zero" and as such will see zero volts.

Now, if you make the positive side of the cap your "zero" by connecting the black probe to it and take a measurement off of the negative terminal of a charged cap with the red wire, you will see a negative voltage. This is because the negative side of the filter cap is negative relative to the positive terminal, which you have just made your "zero" by connecting the black lead to it.

If you reverse it so that the black lead on the meter is on the negative (thereby making negative your "zero") and take a measurement with the red lead on the positive terminal of a charged cap, you will see a positive voltage.

So...voltage is relative to a "zero point" and that zero point is anywhere you reference one side of your circuit to, be it the positive or the negative side of the circuit. If you reference the positive side of a circuit to zero (which we call "ground"), all measurements within that circuit will be negative relative to the zero ground reference. Vice versa if you reference the ngative side of a circuit to the zero ground reference.

[flemingmras]

Back to the original question, why are the largest filter caps in your power supply only fed voltage and then grounded with no other taps?

Not sure what you mean by this one. Most valve amps connect the center tap of the output transformer primary here, which supplies your power tube plates with a positive voltage through each side of its primary.

[noworrybeefcurry]

Thank you, your voltage explaination made sense of everything.

But as far as my second question; here is a schematic for a 5F6-A Fender Bassman http://www.ceriatone.com/images/layoutP ... 100508.jpg" onclick="window.open(this.href);return false;

From what i can see there is a tap off of the power transformers high voltage secondaries to the output transformers primary center tap, a tap going to the choke which feeds further circuits, but their is also a tap (A) going to the two 22uf 500volt caps in parallel which then go directly to ground. What is the purpose of feeding caps just to ground them?

[flemingmras]

Thank you, your voltage explaination made sense of everything.

But as far as my second question; here is a schematic for a 5F6-A Fender Bassman http://www.ceriatone.com/images/layoutP ... 100508.jpg" onclick="window.open(this.href);return false;

From what i can see there is a tap off of the power transformers high voltage secondaries to the output transformers primary center tap, a tap going to the choke which feeds further circuits, but their is also a tap (A) going to the two 22uf 500volt caps in parallel which then go directly to ground. What is the purpose of feeding caps just to ground them?

OH! That's a tube rectifier circuit lol.

Inside of a rectifier tube, one side of its heater is directly connected to its cathode. The 5V heater winding that supplies heater voltage to the heater doesn't see the high voltage though because only one side of its winding is connected to the high voltage supply. It's not referenced to the HT ground...it's "floating" above the "zero ground reference" at HT potential. But since only one side of the 5V winding is referenced there, to the 5V winding it still sees 5V.

Now if you were to reference the other side of the 5V winding to ground you'd definitely fry the winding.

[noworrybeefcurry]

O, sorry for the mix up. But either way, i did not comprehend any of what you said. I dont even know where to start to help myself understand that one.

[flemingmras]

O, sorry for the mix up. But either way, i did not comprehend any of what you said. I dont even know where to start to help myself understand that one.

Perhaps this will help -



Notice that the HT secondary has its center tap referenced to ground. But the heater winding only has 1 connection to the HT supply.

In order for anything to see the voltage on a power supply, it must be connected to BOTH sides of said supply because voltage is relative.However, the heater winding in this circuit is only connected to ONE side of the supply so it doesn't see the "relative to ground" voltage that the HT supply kicks out. Relative to the positive side of the HT supply, one side of that winding is at the same potential as the positive side of the HT supply. But the other side has 5VAC relative to the HT winding and since one side of the heater is ALSO referenced to the positive side of the HT supply, when connected to the other side of the winding it sees 5VAC relative to the positive side of the HT supply. Since it is 5VAC relative to a positive voltage source, this makes it 5VAC with a DC offset equal to the positive HT voltage.

Any positive voltage that is measured relative to a positive voltage source is said to be "floating above ground" since its voltage is relative to a reference voltage that is more positive than ground.

[noworrybeefcurry]

This one is a little hard for me to comprehend, so basically your saying that because the 5VDC is in reference to the high voltage secondaries then it appears to the rest of the circuit as a much more higher voltage than it really is? But if this is so than wouldnt the filament leads actually appear as a much higher negative voltage? Also how can the tap be off of the cathode/filament, isnt electron flow from cathode to plate?

[noworrybeefcurry]

Also, im still not understanding how this ties into the larger filter caps being only grounded?

[Tone Junkie]

So is the positive side of the heater supply connected to pin 8 and the so called negative side connected to pin 2 but in reality pin 2 is not ground its just the other side of the complete circuit for the heater tap. Thanks Bill

[flemingmras]

So is the positive side of the heater supply connected to pin 8 and the so called negative side connected to pin 2 but in reality pin 2 is not ground its just the other side of the complete circuit for the heater tap. Thanks Bill

You got it mostly right, but since it's 5VAC you don't have a "positive" or a "negative" side since the two wires are always changing polarity at 60 cycles per second (i.e. 60Hz). But yes the two wires of that coil on the PT are connected to each side of the heater which completes the circuit...but it's just referenced to the positive side of the HT supply (i.e. the cathode) rather than being referenced to ground.

Noworrybeefcurry, I'll type up an explanation tonight. It's gonna be another long one lol.

[noworrybeefcurry]

Haha, I appreciatte all of your time.

-Thanks

[yladrd61]

So to the best of my understanding filter caps are polarized and when you introduce a high voltage positive current onto the positive side of the cap from your rectifier circuit the filter cap pulls electrons from ground into the cap towards the positive terminal so it can charge? But how does this work, electrons flow negative to positive and is ground not more positive in relation to the negative terminal of the cap?

Secondly what do you mean by the negative side of your power supply? Are the filte caps not running off of a tap from your rectifier circuit which is positive?

Bump