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Old 23rd June 2005, 01:41 AM   #1
abj1 is offline abj1  Australia
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Default Source for common mode chokes

Hi All,

Tired of tooling around on the internet and getting nowhere....

Could someone please be kind enough to point me in the direction of a source for retail quantities of common mode chokes (at say 3mH or greater and rated for 1A or greater)? A source in Melbourne, Australia would be fabulous but then again it's a global economy we live in, eh!

I have half a dozen generously given to me by a friend (thanks a zillion Jeff) and I like what they do for my 56 - 46 - 50 SE amp. However I will likely need more as I get into DC power supplies for battery DH valves for a preamp project, among other things....

Cheers,
Andrew.
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Old 23rd June 2005, 05:25 AM   #2
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Hi,

I get mine from http://www.digi-key.com

If you have a Hammond dealer where you are, you can get them there too, but they are more expensive.
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Old 23rd June 2005, 05:26 AM   #3
rdf is offline rdf  Canada
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You mind telling how you're using them in the circuit? I like what uH air-core coils do in the B+ of my EL84 SE and have considered trying common modes after seeing them in pictures of another member's amp.
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Old 23rd June 2005, 02:25 PM   #4
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Try Farnell and RS
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Old 23rd June 2005, 10:57 PM   #5
abj1 is offline abj1  Australia
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Thanks Brett,

I was hoping someone local would set me straight (there are a surprising number of posters on this forum from south-eastern Australia!) - I'd completely forgotten about Farnell and RS - I'm a bit of a vegetable at times and admit to getting most of my non valve bits from Jaycar and DSE In general I'm a bit cheap and nasty - top shelf audiophile to me means orange drops for coupling caps.....

If no luck I will try Digi-Key (thanks Geek)

Cheers,
Andrew.
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Old 23rd June 2005, 11:17 PM   #6
abj1 is offline abj1  Australia
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Hi RDF,

I did't do anything particularly inventive - I just shamelessly copyied a circuit posted by Kuei Yang Wang a while ago on this forum, using the parts I had to hand. It goes something like this:

Toroid with 7.5V secondaries, SS bridge using 1N5822 schottky (?spelling) diodes, 4700mF electrolytic, 0.1mH air-cored crossover inductor, 4700mF electrolytic, 3mH common mode choke. One supply for each valve, all floating.

The filament power still has around 250mV of ripple and so is introduced to the 50 filaments through the traditional hum pot with the centre tap grounded through the traditional 'cathode' bias resistor. I found that this removed some of the 'lushness' from the sound but without 'drying out' too much. It is very much to my taste and IMHO better than AC filaments (and significantly less hum as well). My take on what is happening is that the harmonics of 50Hz are dramatically reduced which cleans up the upper bass and lower midrange - the other goal apart from hum reduction. I have also done the same thing with the filaments for the 46's driving the 50's except that the caps are 2 x 4700 and the inductor is 1mH rather than 0.1 from a secondary winding of something like 3.5V (I just kept winding on turns until I got 2.5V DC). This has less ripple but still well over 100 mV (can't remember exactly how much). This too gives good results (to my ears anyway). Haven't got as far as a DHT for the input stage yet (currently 56's) but no doubt will have to get a third DC supply in there somewhere - space is getting a tad tight now!

DIY is great - you can muck about as much as you like - whenever you get a new idea and the urge - just go for it and check it out!


Hope this rant makes a bit of sense!
Cheers,
Andrew.
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Old 24th June 2005, 03:01 AM   #7
Kyle K is offline Kyle K  United States
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Try BG Micro in the U.S. They have Panasonic and TDK 3.3mH @ 4.2A common mode chokes for less than a dollar. Search for part numbers PWR1025 and PWR1026. These sell for almost $10 at Digikey.
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Old 24th June 2005, 06:31 AM   #8
rdf is offline rdf  Canada
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Thanks Andrew! My application turns out to be completely different, RF filtering the B+ of a pentode amp. Might be worth trying the one CM coil I have on indirect heaters just for kicks though. Thx again.
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