Effective Capacitance of Lower Filter Cap in Series Pair?

[David Root]

I've looked and looked but cannot find/figure out the answer to the above question.

I am looking at taking the plate supply off the top at x volts and the screen supply off the junction between the caps at x/2 volts. So the plate supply sees an effective capacitance of C1 + C2/4, no problem. For example, two 100uF caps in series gives 50uF effective plate capacitance. But what about the effective capacitance for the screen? Is it 100uF, 50uF, 25uF, or what?

I know the charge on each cap is the same because the current in each is the same, but somehow I can't get to an effective capacitance at the junction of the two caps.

[Reeltarded]

The capacitance between it and ground. In your case, 100u just like you are thinking.

Ummm.. I am trying to imagine other things to consider. Blank.

[David Root]

Yeah, I couildn't either. Intuitively it doesn't seem right that there is 50uF on the plates and 100uF on the screens.
If that's true then I don't need a choke on the screen supply as well, right?

[Reeltarded]

I have never heard of doing such a thing and I am loathe to guess when it comes to supplies.

What's your idea all about anyhow? Sneaky... heh

Oh you are sneaky. How about resistance in place of a choke.. yeah, no you don't need a separate choke. I suddenly get what you are up to.

[JazzGuitarGimp]

Will you be using a full wave bridge with a center-tapped transformer - center tap connected to the junction if the two caps? If not, your screen node may not be low impedance enough to hold at 1/2 B+ under full tilt conditions.

[Firestorm]

The way this is typically done is with a full-wave bridge and a center-tapped transformer, with the center tap connected to the junction of the stacked caps. That way the lower voltage node uses only half the transformer secondary which helps stabilize its voltage more than the parallel resistors would alone (since you are loading that node with screen current demands). You shouldn't need a choke.

[roberto]

Something similar to hiwatt? (Except for the choke)
[img975]http://hiwatt.org/Schematics/DR_200wPS.gif[/img]

[David Root]

Not really, more like a Music Man amp. Only using a conventional full wave arrangement. I can see I need to research tis a bit.

Reason is this is for a 4x6Y6 amp which will use about 250-260V plate and 125-130V screen.

Also will have a 5931 rectifier (5U4WG).

[tubeswell]

Maybe like a half-wave voltage doubler supply for the plates with the screen node taken off the bottom filter cap?

[David Root]

No, full wave thru a tube rectifier, like this:-