Strange filter cap question

[greiswig]

So suppose you have a pair of 50uF caps in series for the first filter stage in the power supply. But the bass is a little flabby. So you try paralleling another pair of 50uF's in with those, for a total of 50uF overall. But that seems like too much: the bass is too tight.

Is there anything wrong with just removing one of those paralleled caps? (i.e. a 100uF in series with a 50uF) Or does this pair need to be symmetrical even though it's in series?

[es345]

this should work.

But keep in mind: at the 50 uF you have 2/3 of the total voltage, at the 100uf 1/3 of the total voltage.

Hans- Georg

[selloutrr]

why not take the bass out at another stage?

i.e replace the standard 25mfd/25v cathode cap with a .68 @ 100 polyester

[Structo]

Try a couple 20-22uF caps in parallel.

[Firestorm]

Assuming you originally put them in series to boost the voltage rating, you'll want to design a voltage divider between B+ and ground to split the voltage appropriately. For example, in the Fender reissue Deluxe Reverb, the main filter is a 220uF/100V in series with a 47uF/500V. The voltage is split between the two with a 100K 1/2W across the 220uF, in series with a 470K 1W across the 47uF.

[Colossal]

Is there anything wrong with just removing one of those paralleled caps? (i.e. a 100uF in series with a 50uF) Or does this pair need to be symmetrical even though it's in series?

Hiwatt used some asymmetry in their cap choices. Check out the HT3 node in the DR100 power supply.

See here:
http://hiwatt.org/Schematics/DR_100wPS.pdf

[greiswig]

Thanks, all...I hadn't considered the voltage divider aspect. Gotta love this place!

[Zippy]

A series/parallel network to dial in optimum capacitance is fine as long as your voltage ratings are up to the task. If not, then the voltage divider approach is prudent.

[David Root]

Look at the '70s (original) Ampeg SVT power supply, I found it educational.

[Super_Reverb]

So you try paralleling another pair of 50uF's in with those, for a total of 50uF overall. But that seems like too much: the bass is too tight.

It sounds as if you might be saying, you want more sag? Are you using silicon diode rectifiers? IF so, could add small resistor in series with rectifier.

If you want to tailor bass response, selloutrr's idea of adjusting cathode bypass value or maybe smaller coupling caps would get you there.

cheers,

rob

[Cliff Schecht]

Look at the '70s (original) Ampeg SVT power supply, I found it educational.

What schematic are you looking at?

[greiswig]

Okay, a related question: this is on a non-stock D'Lite build. The original 2x6L6 build used that pair of 100uF caps for the initial filter stage. Now, however, I've upped the plate voltage, moved to a 100W OPT, and am running a pair of KT-88s.

So...what should I be running as that first filter stage capacitance, or is the capacitance at all related to the output power that you are going to be producing?

If I look at #124, for example, it's got 150uF at that stage, or 3x the amount I've got, and #124 is a 100W amp. Mine is producing probably 80-90W.

[Structo]

George on my 100w amp I used two 320uF caps.

[img:640:540]https://lh4.googleusercontent.com/_MHnI ... G_0676.JPG[/img]

[greiswig]

So you're saying that more power output requires more capacitance at this stage?

[David Root]

Cliff, see below, out of SchematicHeaven.