OT Lead Dress; pri vs. sec

[JazzGuitarGimp]

So, in thinking through this, it occurs to me that the more current you pass through a wire, the more magnetic field will be present around the wire. As this relates to the output transformer wire lead-dress, am I correct to conclude the secondary wires will get me into more trouble (because of bad lead-dress) than the primary wires?

Many thanks,
Lou

[Firestorm]

That's a pretty interesting question. I guess if you do something galactically stupid with an OT secondary it would be a problem, but it's typically the power amp grids that cause grief. Have to think on that some more.

[JazzGuitarGimp]

Hi Firestorm,

Thanks for your reply.

I am thinking of the OT leads as transmitters. Which would be more detrimental; having the OT primary leads near the output grids, or having the OT secondary leads near the output grids? In doing pcb layout work, I've learned to keep sensitive input traces short - stands to reason, and this ethic directly translates to a hand wired tube amps as well. But what I am trying to understand, and I apologize because after thinking about it more, I should have said this in the original post, is this: If the output transformer could be positioned and oriented such that one set of leads (input and output) is shorter than the other, which would be best to keep short?

THanks,
Lou

[Firestorm]

In a standard octal output tube, the grid and plate connections are half an inch apart (and internally closer than that) but out of phase. The secondaries are usually a couple of inches away (and don't mind being twisted) so I think you're boiling the ocean (as my old IBMer friends used to say). The standard layouts seem to work.

Still, an interesting question, though.

[Tillydog]

I think the answer depends on whether you're more concerned with magnetic or electric fields. Higher currents give higher magnetic fields, but higher voltages give higher electric fields.

Empirically, it's the primaries that you need to be more worried about.

Andy

[Firestorm]

I think the answer depends on whether you're more concerned with magnetic or electric fields. Higher currents give higher magnetic fields, but higher voltages give higher electric fields.

Empirically, it's the primaries that you need to be more worried about.

Andy

Oh, now you've opened a can of worms. I have physicist friends who will dispute that there is any meaningful distinction between an electric field and a magnetic field. But I am not smart enough to take this up. Cheers.

[JazzGuitarGimp]

The light bulb just went on. Thank you, Andy.

I was not aware that there was a distinction between the magnetic field and the electric field. After I read your post, I went out to Google (my second favorite place after TAG) and did a little research. I now understand how fluorescent lights play so much havoc with guitars and amps. Fluorescent lights are very low current, but they run at very high voltage. The higher the voltage, the higher the "electric field".

Making more sense now.....

Thanks again.

[VacuumVoodoo]

Just put grounded screen on both primary and secondary flying leads and stop worrying

[IMG:556:262]http://i26.photobucket.com/albums/c149/ ... ceened.jpg[/img]

[LeftyStrat]

Just put grounded screen on both primary and secondary flying leads and stop worrying

Brilliant!

[boots]

That's beautiful Voodoo!

I actually just did some OT swapping in one of my single-ended 6BQ5 amps. I made sure to twist the wires of the primary AND secondary just for good measure. I wondered the whole time though, if it was really necessary to do that. I figured it couldn't hurt.

[Reeltarded]

HAH! Badass!

[ChrisM]

Just put grounded screen on both primary and secondary flying leads and stop worrying

[IMG:556:262]http://i26.photobucket.com/albums/c149/ ... ceened.jpg[/img]

Where can someone get some of this grounded screen?

I see many builders braid/twist the leads then shrink wrap them but this is new to me.

[Tillydog]

I have physicist friends who will dispute that there is any meaningful distinction between an electric field and a magnetic field. But I am not smart enough to take this up.

Me neither! I guess they're just different manifestations of some fundamental thingumajig. As an engineer, I'm happy to consider them as separate thingamajigs (stop me if I'm getting too technical...)

Case in point: We twist the high current AC leads for the heater supply, but don't bother screening them; we screen signal leads, but don't bother twisting them (mostly).

Incidentally, the cool-looking shielding over the OT leads will reduce electric field intensity, but not the magnetic.

Andy

[M Fowler]

Also, you can route the OT wires above the chassis to designated area rather then under boards inside the chassis.

Mark

[VacuumVoodoo]

Incidentally, the cool-looking shielding over the OT leads will reduce electric field intensity, but not the magnetic.
Andy

No need to worry about magnetic fields. If you consider two current carrying wires, even twisted, to be a transformer, then it's a very poor transformer because it has core made of plastic and air. In our applications it really is a "transformer that is not". Electric fields don't need an iron core, think radio transmitter. Very simplistic explanation, evidently.
Screening and shielding is employed to either prevent an interfering field from entering a sensitive circuit or prevent from escaping its source.
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