Question regarding 5e3 build

[Nemesys]

Greetings,

I am starting to build a 5e3 using the Weber schematic and layout (found here and here, respectively). As a first step, I am verifying that the schematic and layout are consistent with eachother, and I found one difference: the schematic specifies that pin 3 of V3 connects to the OT primary via the brown wire, and pin 3 of V4 connects to the primary via the blue wire. The layout has these connections reversed. From what I know of tube circuits, the amp should work fine either way I make the connection; though reversing the connection would result in the sound being 180 degrees out of phase with what it would have been otherwise. However, I'm a beginner when it comes to building amps, so I'm posting here to ask, am I correct with regard to this particular issue, and if not, can someone tell me which way of connecting the OT is correct? If I'm not correct, I would also be interested in knowing where my misconceptions lie, as I am trying to learn as much as I can about how tube amps work, it's a fascinating subject to me.

Thanks in advance for any help which anyone can provide!

[hasserl]

It really doesn't matter which way you connect it, either way will work fine. On an amp with negative feedback this can cause a problem if not connected correctly, as the nfb then becomes pfb (positive feedback). But in this case, no NFB, no problem.

[Nemesys]

Thank you, kind sir!

The "negative feedback becomes positive feedback if the OT is wired backwards" issue must be why, on some of Weber's designs with negative feedback, such as the 5E8A, for example, there is a notation on the schematic which says, "If loud oscillation occurs, reverse blue and brown wires."

[hasserl]

Yep, you got it. The positive feed back wil cause a loud oscillation that can scare the crud out of you. Reverse the OT wires to correct it.

[Steve A.]

It really doesn't matter which way you connect it, either way will work fine. On an amp with negative feedback this can cause a problem if not connected correctly, as the nfb then becomes pfb (positive feedback). But in this case, no NFB, no problem.

Technically correct, but other factors can contribute to some coupling between the various elements. A highly-regarded amp builder here will try reversing the OT connections even when NFB is not used- sometimes you *can* hear a difference. (This would usually be a subtle difference, not the howling associated with a NFB loop connected backwards.)

Merry Christmas!

Steve Ahola

http://www.blueguitar.org/

http://www.myspace.com/steveahola

[Chuck H]

I'm going to back Steve on this. Not based on my experience with swapping OT leads, but on swapping guitar pickup polarity. If you switch the polarity on a single coil pickup you will hear a difference. Subtle but there. I can imagine that an OT would do the same. I'm guessing signal phase alignment. Amp plays foreward or backward. That will change the harmonics and response character. I have one build right now with a switchable in line effects loop. If I use a straight cord (nothing in the patch), switch the loop in and out while sustaining a harmonic, the harmonic will cease and then return as a different harmonic. There is otherwise no change whatever in the tone. So I have to believe that it's the phase of the signal (which reverses 180* when the loop is switched in) that is doing it.

Chuck