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Chokes in the ground "plane"
Chokes in the ground "plane"
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Old 17th June 2013, 09:36 PM   #11
Bas Horneman is offline Bas Horneman  Netherlands
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Fixed the center tap.
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Last edited by Bas Horneman; 17th June 2013 at 09:41 PM.
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Old 17th June 2013, 09:49 PM   #12
Frank Berry is offline Frank Berry  United States
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Correct.
Many broadcast transmitters were designed with the choke on the negative leg of the power supply.
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Old 18th June 2013, 05:09 AM   #13
maxro is offline maxro  Canada
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Does this method affect the amount of capacitance "seen" by the rectifier? Ie: does the first choke in the ground run isolate the caps after it from the rectifier as it would if the choke were in the HT line? If not, I could see this as a major gotcha what with exceeding maximum capacitance for a valve rectifier.
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Old 18th June 2013, 06:57 AM   #14
Vinylsavor is offline Vinylsavor  Germany
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Quote:
Originally Posted by maxro View Post
Does this method affect the amount of capacitance "seen" by the rectifier?
No

Thomas
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Old 18th June 2013, 09:40 AM   #15
trobbins is offline trobbins  Australia
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Originally Posted by Vinylsavor View Post
I read about one disadvantage of this approach:
You have some stray capacitances from the transformer secondary to the core and thus to ground. This stray capacitance is in parallel with chokes in the ground return and thus bypasses them.
Some PT's have an electrostatic or protective screen between primary and secondary, and the screen is normally grounded to chassis. The capacitance from secondary HT to screen may conduct mains frequency and diode rectifier related noise depending on the winding section next to the screen.

Similarly, edges of winding layers and the outer layer (usually the secondaries are on the outer layers) have parasitic capacitance to core (and hence to chassis).

Effectively, the filter capacitors are short circuits to mains and higher frequency noise, and such noise currents simplistically loop via the stray parasitic capacitance to chassis to star ground and back to the secondary windings via the CT and diodes. The chokes per se are not going to significantly suppress this form of noise, or affect it.
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Old 18th June 2013, 02:13 PM   #16
Tom Bavis is offline Tom Bavis
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Any additional common noise on the B+ due to this connection can be easily dealt with - since it's primarily high frequency noise, a small RC section in the positive lead will handle it. or put one choke in negative lead, one in positive.

It's a series circuit, so order of components doesn't matter (to first order).
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Old 18th June 2013, 08:24 PM   #17
Hearinspace is offline Hearinspace  Canada
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Chokes in the ground "plane"
Quote:
Originally Posted by Vinylsavor View Post
Hi!

I read about one disadvantage of this approach:
You have some stray capacitances from the transformer secondary to the core and thus to ground. This stray capacitance is in parallel with chokes in the ground return and thus bypasses them.

How relevant this effect is? I don't know. Your chokes have some winding capacitances too. So it probably depends on the transformer.

I'd get proper chokes which can handle the voltage.

Best regards

Thomas
Sounds different too. I tried variations of this with both single winding chokes and Lundahls in their common mode configuration. It was years ago and my preferences may have changed since then but at the time I didn't like what I heard. I remember the common mode connection in particular made the circuit sound smooth but lacking life - a little like the effect of voltage regulated filaments. () Not an EE but my thought was that putting resistance in the return to the rectifier might not be a good thing. That's how I left it anyway.

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I may be wrong, but the schematic in post 4 does not look correct to me.
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Old 22nd June 2013, 02:19 AM   #18
wa2ise is offline wa2ise  United States
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Oh, you'll find that the transformer centertap will have a DC voltage of something like 15V, with lots of ripple. Depending on choke inductance, resistance and current draw off the B+. You probably don't want to use this 15V for anything, as there is that hazard if the chokes ever go open...
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Old 22nd June 2013, 05:22 AM   #19
hpeter is offline hpeter  Slovakia
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Originally Posted by nigelwright7557 View Post
Should a choke go open circuit you could end up with high volts on the input jack ground and kill someone.
no
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Old 22nd June 2013, 05:41 AM   #20
hpeter is offline hpeter  Slovakia
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Quote:
Originally Posted by maxro View Post
Does this method affect the amount of capacitance "seen" by the rectifier? Ie: does the first choke in the ground run isolate the caps after it from the rectifier as it would if the choke were in the HT line? If not, I could see this as a major gotcha what with exceeding maximum capacitance for a valve rectifier.
rectifier currents go red lines, not blue
----------
this connection has one big benefit, its the Umax winding-iron insulation.
supply chokes are often low resistance (across winding), low U drop animals, therefore risk of breaking winding is low

spike across winding could occur with silicon diodes during startup (empty caps, 0 ohm & no softstart), but then put varistor to be sure
but that will happen no matter where you put chokes
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