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dshortt9 14th March 2009 03:38 PM

Can I reverse leads on an OT?
I'm thinking of using an UL SE OT, reversing the primary leads so the 40% UL tap becomes a 60% tap. It seems to me that the resulting curve would have less distortion while retaining the higher power output. Reference the 43% vs. 70% curves at this link:

Im using a Hammond 1627SEA with parallel EI KT90's if it makes a difference. Of course I would have a lower damping factor than in triode but still reasonable as SE goes. This design would give me 20 to 30 watts without resorting to higher voltage tubes and the added complications.
I've used a single 300B with my speakers which is adequate most of the time but sometimes I want to turn it up to 11.

SY 14th March 2009 03:48 PM

I'm not following how you're intending to do this. Isn't the percentage referred to the ends of the primary versus the centertap?

Miles Prower 14th March 2009 04:18 PM

I don't see a problem with doing that. The only question remaining is does it sound any good? The one thing I don't like about Ultralinear is that you have very little ability to adjust it. Once the OPT is wound, the die is cast, and all you can do is hope that they got it right.

Try it both ways and see if it makes a difference, and which way you like it best.

dshortt9 14th March 2009 04:50 PM


I'm using a single ended OT and changing the plate lead to B+ and the B+ to the plate. I think this would change the UL% as stated but I could be wrong. Am I changing the 40% tap to 20%?That's why I like to ask first.


Yes, it is fixed when the transormer is wound, otherise I might use a different %tap also.

SY 14th March 2009 05:27 PM

Ahh, sorry, I skipped right over the "SE" part.

Well, the strays will be different and the electromagentic coupling to nearby components likewise, but as Miles said, try it, ya never know.

dshortt9 14th March 2009 05:40 PM

strays will be different and the electromagentic coupling.

That's the part I didn't think of. Gotta just try it.

Tubelab_com 15th March 2009 03:21 AM


I'm thinking of using an UL SE OT, reversing the primary leads so the 40% UL tap becomes a 60% tap.
Yes, you can do this, and it will work electrically. As stated the stray capacitances will be different than the normal connection. Nothing bad will happen, but the results may be slightly different than you expect. I have swapped the ends on several different OPT's with varying results. I have not tried the 1627SEA since I don't have any of them. The 1628SE sounds like *$%# no matter how you connect it, The 1628SEA is better.

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