Question about proper choke values - diyAudio
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Old 28th November 2001, 01:47 AM   #1
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Not so much about value of inductance,but how to choose one with the correct current rating.The project I'm looking at is a PP 6550 amp,triode connected,so there's 150ma just at idle and 210 for peak,plus another 30ma or so for the front end tubes.So I don't think a 300+ma power supply is overkill.Besides,I like overkill,large cubic inch engines,lotsa horsepower.To my way of thinking,this would help lessen the need for regulation.I'm looking at using either the One Electron power tranny(385v,300ma) or perhaps something from Peter Dahl.Would also like to use twin rectifiers,tube of course,and feed this into a pi type filter.So how do I find the right choke,current wise?Hopefully something from the Hammond catalog.Any help is greatly appreciated.
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Old 30th November 2001, 02:29 PM   #2
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John,
I like having a bit of elbow room on things like this. For my amps (4x6550, 130W, idle current for the back end about 200mA) I used a Stancor C-2708:
.32H
600mA
10 ohms
Yes, I know, Stancor isn't politically correct in the audiophile community, but it sounds just fine. They're also inexpensive (by virtue of not being annointed with snake oil). I paid about $7 each for mine.
As an aside, you might want to consider a somewhat heftier power supply. If your circuit draws as much as 250mA on peaks, 300 mA will be cutting it close. Your transformer will probably run hot to the touch. I used the 465mA Hammond power transformers and plenty of capacitance, and mine still get warm.

Grey
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Old 30th November 2001, 03:00 PM   #3
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I was hoping to use tube rectifiers if possible.Probably doubling them up.Either 5AR4 or 5V3,but I realize the HV filament demand also.Might have to go with a tranny from Peter Dahl.They'll do most anything with iron and wire.So you think that double the peak current is a good target value?Should be no problem with headroom.
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Old 30th November 2001, 03:26 PM   #4
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John,
Seems that power transformers almost never have enough current capability on their filament windings for whatever you want to do. Consider the idea of a separate filament transformer. It'll free up your options on rail voltage/current combinations. I generally run the front end tubes off the filament windings and the power tubes off a separate transformer. Unless you're hell-bent on having a custom transformer wound, it'll save you money. Keep in mind that lots of the commercial amps have separate filament transformers; sometimes they're tucked underneath the chassis where you can't see them.
I'm not an expert on tube rectifiers--I use solid state--so I'm not going to be able to suggest much on same without spending a lot of time in my tube books.

Grey
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Old 1st December 2001, 11:05 PM   #5
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I plugged that choke into PSUD and didn't see any thing strange happen.After considering both approaches,I like the vacuum rectifiers ability to turn on a little slower.Yes,maybe there's a little loss in ultimate bass slam.But I'll never worry about puking a filter cap.I like something that's reliable and simple.The problem is really that there are no perfect circuits or components.One has to deal with a set of compromises at every turn.Trying to balance a set of values, so that simplicity doesn't compromise quality,is something that can be very frustrating.Sounds like Robert Pirsig stuff - Zen and the Art of Audio Design or How To Please Your Ears and Become Certifiably Crazy.
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Old 2nd December 2001, 03:18 AM   #6
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Some people swear that tube rectifiers sound better. I have no opinion, as I've never put it to the test. You may end up ahead that way.

Grey
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Old 2nd December 2001, 04:08 PM   #7
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Now that I found the rest of the Hammond catalog,I see they have a lot more than I realized. I can see that what I want to do is feasible and parts are available,I'll fine tune circuit ideas to suit.Looking at a 5751 long tail splitter into a 5687 diff/driver for PP 6550's.Thanks Grey,JPS.
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Old 3rd December 2001, 03:34 AM   #8
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Default Rectifiers

John,
You might want to take a look at 5V4s intead of 5AR4s as they are soft start and easier on the rest of your tubes. I also like chokes in the power supply to stop the AC ripple and if you have lots of room think about those big flat can caps used for electric motors. They don't have a lot of uf but you don't have to worry about zapping them. I am planning on using some of those and chokes to take care of the ripple and then using an electrolitic for the capasitance. I have a pair of huge chrome chassis from the 40s and plan on building a PP and a SE with a tube active cross on each one. The original amp used the same power supply for a PP 5881 and a separate preamp so it has 2 rectifiers and 2 chromed potted chokes that are 5.5 Hnry each. This is one of those way down the road projects though.
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