"Stock" PI-Filter Choke Construction

Hi,

I've found a tame coil winder near me who's reasonably priced. I have a few small signal valve projects coming up, so I thought I might see about getting some 'stock' chokes wound to use in pi-network PSUs. The idea being that I can employ the chokes on a variety of projects, be it preamp, EQ or compressor etc.

The winder makes everything to order. He doesn't really get involved in the design process. He's got a well equipped factory with CNC gear and makes custom designs for respected audio OEMs. Can anyone give me a starting point for the kind of lams I should look for? I'm thinking something around 10-20 Henries with 10-20mA of handling @ <200R DC resistance - would this constitute a good "stock" PSU choke in your book?

Many thanks in advance.

Justin

silicon steel is used in most chokes, 0.014 

coil construction for a pwr supply choke is simply a start and a finish on one bobbin,

no fancy winding required, can be random wound

i forget which end gets the B+,

really does not matter as both ends have about the same voltage on them

what kind of projects are you going to power?

thermionic said:

Hi,

I've found a tame coil winder near me who's reasonably priced. I have a few small signal valve projects coming up, so I thought I might see about getting some 'stock' chokes wound to use in pi-network PSUs. The idea being that I can employ the chokes on a variety of projects, be it preamp, EQ or compressor etc.

The winder makes everything to order. He doesn't really get involved in the design process. He's got a well equipped factory with CNC gear and makes custom designs for respected audio OEMs. Can anyone give me a starting point for the kind of lams I should look for? I'm thinking something around 10-20 Henries with 10-20mA of handling @ <200R DC resistance - would this constitute a good "stock" PSU choke in your book?

Many thanks in advance.

Justin

Click to expand...

For small signal work that value fits the bill for a typical PS choke.  I don't think they're as critical in voltage amps as they are in big power amps though Langevin and WE have used them on some 1 watter 6v6 line amp circuits.

They're handy for dropping excess voltage off an overrated PT - ~50V. 

For what you can buy them from Hammond for - 18.00 -I'd vote for seeing if your winder can wind you some nice high inductance plate chokes instead   

holy crap, i called this utc a traid, 

too many threads at once, i guess,  ;D

http://www.groupdiy.com/index.php?topic=36493.0

oh yeah, the most important thing,

you need to gap the core with some kraft paper,

> 10-20mA of handling @ <200R DC

Why do you need 10+H with under 4V DC drop?

That inductance suggests >5K audio impedance. At 10-20mA you must be expecting 50-100V somehow. And probably several hundred? So starting from 200V, what's the difference if you get 196V or say 180V?

Also a 10K AC impedance with a 200r DC impedance suggests a Q like 50, which is mighty high for a simple iron-core coil. It may not be possible with a reasonable lump of silicon steel carrying DC. It won't be affordable in Permaloy, even before you bulk-up to handle the DC.

If you can get an AC/DC impedance ratio near 10, you are doing a lot better than an R-C filter, yet with a practical choke.

If you can custom-wind, wind your PT HV up 10%-20% from what you need. Then you can take that 10%-20% back down in higher-resistance chokery. While this adds 5%-10% to PT cost, it may save a bunch in choke cost, or make an impossible design trivial.

BTW: the larger stock "Fender replacement" guitar amp chokes will carry 20mA and are nearly 10H at under 1K DCR. Unless your guy just loves to throw wire at a loss, he probably can't match the cost of low-pay imports, even with transport and dealer markup.

>what kind of projects are you going to power?

A variety of small signal projects, ranging from mics to compressors

>For what you can buy them from Hammond for - 18.00 -I'd vote for seeing if your winder can wind you some nice high inductance plate chokes instead

I didn’t realise Hammond sold them so cheaply. Will check them out. I looked into Plate Chokes. I’m sure he could make them. However, they’re more tricky to get right than PSU chokes. Secondly, it’s difficult to have a ‘stock’ plate choke as they have to suit the Rp of the tube being used.

>Why do you need 10+H with under 4V DC drop?

I don’t. Not sure what made me think that. Your logic makes sense. I can always specify a higher secondary voltage.

Thanks to all of you.

Justin