Another mundane power tranny question...

Eoin · Post by **Eoin** » Sun May 22, 2005 11:24 am

dynaman wrote:What about the first cap's value? I know the size of this cap affects what the final voltage will be. Anybody know the formula?

Afaik, nobody here knows the formula - I asked about this before! Unfortunately Googling did not turn up the information for me either, so I remain without an answer for the time being.

Flames1950 · Post by **Flames1950** » Sun May 22, 2005 1:19 pm

I don't know of any formula. How much filtering do you want there? As little as you can get away with? Enough to ensure tight low end sound and no ghost notes?
Gerald Weber seems to like at least 100uF for the first filter for plenty of reserve current, but I'm sure that's an opinion and not based on any mathematical formula.

Eoin · Post by **Eoin** » Mon May 23, 2005 8:23 am

Well yeah, but the formula is not to decide what you like, it's to establish what the implications of your choice will be on the voltage in the circuit.

Flames1950 · Post by **Flames1950** » Mon May 23, 2005 9:00 am

There is little or no implication on the voltage of your circuit, the filter caps shoot off as a parallel branch and hence you see the same voltage on both branches. It's the decoupling resistors that are going to drop your voltage on the B+ rail.
I've upped the filtering in almost all my amps at one time or another with no noticeable implication on my plate voltage. At least until I rack 'em out on ten and my voltage doesn't drop since I have enough current reserve, thanks to my adequate filtering.

Eoin · Post by **Eoin** » Mon May 23, 2005 9:11 am

What is the relationship between current and capacitance? For example, if you drop the max current in the amp from 500mA to 50mA, what is the proportional change (if any) in the filter cap values required to achieve the same filtering?

Eoin · Post by **Eoin** » Sun May 29, 2005 9:22 am

Seriously, does anyone know? This one's been bugging me. The only formula I could find applies to a filtered circuit containg a voltage regulator.

Billy Batz · Post by **Billy Batz** » Sun May 29, 2005 5:53 pm

You dont drop current. Each section of your amp that draws power draws a certain amount of current and your Tranny can provide that or not. Its not like voltage where you can alter the numbers but if you look each tube type has a specific spec. As far as I know, in an amp circuit, the changes your refering to are negligable. Theirs no reason to stress. The simplest thing to do is just start with the common 50 for the mains and screens and if you have any trouble you can up them both or try uping the mains to 100 first.

Eoin · Post by **Eoin** » Mon May 30, 2005 8:12 am

The value of capacitance required has to relate to something, surely?

Billy Batz · Post by **Billy Batz** » Mon May 30, 2005 5:48 pm

How quickly and efficiently it supplies voltage to the amp. If your looking for strict numbers in that regards I cant help you. You can ask the guys at Ampage.org. Their much more technically minded.