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Old 22nd September 2012, 07:12 AM   #2571
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Ok then, i was looking for much bigger inductance
Those ill find at home in a drawerand will give it a try. I was planning to use a resistor but choke is a nice option too then.

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Old 22nd September 2012, 07:24 AM   #2572
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The choke you show is a macro shot of a rather small common mode choke - probably height about 50mm total.

If I was building valve amps I would try a resistor in series with a small choke
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Old 22nd September 2012, 04:05 PM   #2573
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Quote:
Originally Posted by mikelm View Post
The choke you show is a macro shot of a rather small common mode choke - probably height about 50mm total.
And with a ferrite torroid core - not a good choice if you're running DC

Probably one of the most approachable articles is Input Choke & Resonant Choke Power Supplies for RF Linear Amplifiers (by Tony IØJX & Pesa IKØHIT)

If you do the math you'll find you don't need much inductance for deep Class A sand amps as long as the core is big enough not to be completely saturated: a 12VAC or there abouts secondary EI transformer of about the same size as your mains transformer will likely be in the right ball park.

Try it and measure the results.

Last edited by thoglette; 22nd September 2012 at 04:14 PM.
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Old 22nd September 2012, 04:21 PM   #2574
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Originally Posted by thoglette View Post
Try it and measure the results.
There's also a thread on estimating transformer magnetic behaviour here
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Old 22nd September 2012, 05:51 PM   #2575
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Quote:
Originally Posted by thoglette View Post
And with a ferrite torroid core - not a good choice if you're running DC
Well, it's just fine with DC if you run it in common mode as it's designed for - because the opposing currents cancel the flux - but I guess that may not be what you need.
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Old 23rd September 2012, 02:46 AM   #2576
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Thanks for the comments!
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Old 23rd September 2012, 09:42 AM   #2577
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Quote:
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Well, it's just fine with DC if you run it in common mode as it's designed for - because the opposing currents cancel the flux - but I guess that may not be what you need.
Not in this case
Even a full wave rectifier/split rail solution would end up with DC in the core. I think?!
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Old 23rd September 2012, 09:54 AM   #2578
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What case ? I thought he wanted a choke for a tube amp but I have not seen the schematic so I cannot comment about any case . . . .

Just saying if you using this common mode choke as intended the DC currents cancel and that's why the core can be so tiny for such large currents.

As it was not intended for a tube design it might not be very relevant to the "case" whatever it might be
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Old 23rd September 2012, 08:30 PM   #2579
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Quote:
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What case ?
Sorry - I thought we were talking about a JLH amplifier. Ergo single rail, 2 amps (per channel) at 36+volts I clearly missed something somewhere
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Old 23rd September 2012, 08:33 PM   #2580
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Yes, and a choke instead of a resistor in a power supply with a capacitor-resistor (or choke)-capacitor.
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