Pie Filter

[C Moore]

With a pie filter of 10/450 -Choke- 10/450.....
I am building (trying to) an amp from an old piece of test equipment.
The amp will use a 6X5 rectifier tube, and 2 6K6 power tubes. Hopefully I will have enough room to go with a fixed bias.
Anyway..... the 6X5 says it like to see a max of 10 Mics for a reservoir cap. I am wondering if that is kind of small for the first filter stage. I was thinking that 20 Mics might be better. So I am wondering, can the reservoir cap JUST be a reservoir, straight into the choke, with no direct filtering duties.?
That is to say, can I take my first filter stage, for the OT CT, from the second filter cap. The cap that comes after the choke.?
Thank You

[Jana]

You can take the power for the OT center tap from after the choke--provided you have a choke that can handle the full current load.

[C Moore]

You can take the power for the OT center tap from after the choke--provided you have a choke that can handle the full current load.

OK. Thank You.
Then I need to do some math, and see if there is a mA spec for this old choke.
Sorry to ask, but do I consult the RCA manual, then look for the Anode Current spec of each tube.?
Thanks

[Cliff Schecht]

10uF is fine for a small push-pull amp. A single-ended amp might buzzzzz even with a pi filter but the push-pull set should cancel some hum if you match the output tubes decently close. Merlin has a neat rule about power supply filtering that I wish I could find the quote of but I can't. It's something like you take the numbers from the caps in a CLC (pi) filter, drop the uF and add the numbers together. Multiply this value by the inductor value. Your final value should be over something like 200 to be considered adequate filtering. For example, with two 10uF caps, you need 200/10 or 20H of filtering (in this case I'd use the 16H chokes I have laying around). This seems high and I might be wrong sosomeone please correct me if this is the case!

[C Moore]

OK..... so you think I will be fine with just 10 Mics for the pair of P-P 6K6 power tubes.?
The Sig Gen ran ALL of the filtering from after the choke, like I was wanting to do. But I have added one extra 6SL7 fro Trem, so I am not sure if the little choke will handle the current or not.
Anyway, maybe I should just try running the OT CT from the first cap of the pie filter and see how it goes.
Just about NOTHING from the original layout fit the amp I am "building". So, I have a feeling that the pie filter scenario will prove to be the least of my worries.
Thank You
Chip

[Structo]

I hate being a spelling cop but since this is a technical forum.

It's PI as in ∏
Or approx. 3.1416

I believe the PI filter is named because of the shape of the Greek letter ∏

[C Moore]

I hate being a spelling cop but since this is a technical forum.

It's PI as in ∏
Or approx. 3.1416

I believe the PI filter is named because of the shape of the Greek letter ∏

You are, almost, absolutely correct. I added the 'e' but should have used a smiley at the end. My mistake.
Actually, I believe it is Pi.....not PI.
best

[tubeswell]

Merlin has a neat rule about power supply filtering that I wish I could find the quote of but I can't. It's something like you take the numbers from the caps in a CLC (pi) filter, drop the uF and add the numbers together. Multiply this value by the inductor value. Your final value should be over something like 200 to be considered adequate filtering. For example, with two 10uF caps, you need 200/10 or 20H of filtering (in this case I'd use the 16H chokes I have laying around). This seems high and I might be wrong sosomeone please correct me if this is the case!

Halfway down this page:

http://www.freewebs.com/valvewizard1/smoothing.html

"A rule of thumb is that the sum of the two capacitors (in micro-Farads), multiplied by the inductance of the choke (in Henrys) should equal 200 or more for excellent performance."

[Structo]

I hate being a spelling cop but since this is a technical forum.

It's PI as in ∏
Or approx. 3.1416

I believe the PI filter is named because of the shape of the Greek letter ∏

You are, almost, absolutely correct. I added the 'e' but should have used a smiley at the end. My mistake.
Actually, I believe it is Pi.....not PI.
best

Fair enough.

Yeah, it's Pi but emphasized the i.