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Old 5th August 2012, 04:18 AM   #1
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Join Date: Mar 2005
Location: Los Angeles, California
Default Twisting the leads of filter choke

two questions:

Is it a good practice to twist the leads of :

A. filter choke ( 5 inches away from filter caps)
B. Push-pull output transformer primaries (plates and screen grids 4-5 inches away from the tube sockets) together?

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Old 5th August 2012, 04:39 AM   #2
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Join Date: Jun 2012
Originally Posted by audiohead View Post
two questions:

Is it a good practice to twist the leads of :

A. filter choke ( 5 inches away from filter caps)
B. Push-pull output transformer primaries (plates and screen grids 4-5 inches away from the tube sockets) together?

Twisting the leads of the filter choke will make for a neater appearance, but not much else. I twist my leads to keep it clean.
Twisting the primary of the OT will cause a small amount of cancellation, and a small amount of high frequency loss, but it's really small. Basically the same as putting a very small capacitance between the plates of the output tubes. Since the two fields are out of phase, it may help a bit in reducing coupling to other parts of the circuit. OR it may help reduce spurious high frequency noise and reduce the hiss "a little"...especially in the very highest frequency range.
But mainly I am thinking of keeping the wiring neater where possible.
You might have better luck twisting the heater wires. When the heater is AC, it helps confine the fields around the wires, (since the two fields are out of phase, you can realize some cancellation) and reduces the AC noise in the circuit. This really is a good idea, and you have seen most builders dress their AC heater wires this way.
On a circuit board, you will often see the heater tracks side by side, closely spaced together. The designer might be thinking the same thing about reducing the AC noise...but not as effective as twisting the wires.

What's really ignored a lot is that the parts and wires "talk" to each other.
There are a lot more signal paths than the wires. It's really complex...there are signals traveling through the air.
If two wires are placed side by side, it's just the same as connecting them together with a capacitor.

If we built the amp, with all the parts separated, and no coupling through the air, between wires and parts, the amp would sound quite different.
It's just as much the layout, as it is the "electronic" design of the amp itself.

Study the layout of McIntosh tube amps. Study the layout of the "real" original Vox amplifiers. (not the Chinese copies)
These guys had their parts locations down to a science, reducing both noise and unwanted distortion. Bloody geniuses, I would say.

Check out how McIntosh integrated the cathode connections to the power tubes, into the output transformer. (MC225)
This produced the lowest distortion tube amp ever made, just by twisting those wires together in the output winding.

Last edited by soundguruman; 5th August 2012 at 05:08 AM.
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Old 6th August 2012, 01:17 PM   #3
DF96 is offline DF96  England
diyAudio Member
Join Date: May 2007
For HT filter choke and OPT wiring I would use very loose twisting, to reduce loop area without introducing too much extra stray capacitance. Heater wires need tight twisting.
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