Hi:

Although I'm pretty comfortable with the internal workings of tube audio
equipment, up to now I've left transformers to the pros. I decided to take
the plunge into output transformer basics by attempting a rewind on a bad
one in a forgettable and expendable cheap PP mono amp (one section of the
primary was open). I was able to get the transformer apart and reverse
engineer the original winding schedule and have rewound it per original.
As I get ready to reassemble it the question is how the laminations were
stacked. The original E-Is were stacked in a 3x3 pattern. I've seen a lot
of commercial OPTs with a 2X2 arrangement and at least one cheap one as
20X20. I've never seen an OPT with 1X1 but I have seen PTs with that
arrangement. Is there any advantage to restacking in a different pattern.
What's the basis for a pattern other than 1X1? Any general guidelines for
this? I recall seeing a side discussion on this subject a while back but
couldn't locate it and am not sure it was even on RATs.

Thanks
--
Steve

I dunno if their is any advantage, but I do all of mine 1x1

--
Gregg
*It's probably useful, even if it can't be SPICE'd*
http://geek.scorpiorising.ca

Steve, O'Neill wrote:

Hi:

Although I'm pretty comfortable with the internal workings of tube audio
equipment, up to now I've left transformers to the pros. I decided to take
the plunge into output transformer basics by attempting a rewind on a bad
one in a forgettable and expendable cheap PP mono amp (one section of the
primary was open). I was able to get the transformer apart and reverse
engineer the original winding schedule and have rewound it per original.
As I get ready to reassemble it the question is how the laminations were
stacked. The original E-Is were stacked in a 3x3 pattern. I've seen a lot
of commercial OPTs with a 2X2 arrangement and at least one cheap one as
20X20. I've never seen an OPT with 1X1 but I have seen PTs with that
arrangement. Is there any advantage to restacking in a different pattern.
What's the basis for a pattern other than 1X1? Any general guidelines for
this? I recall seeing a side discussion on this subject a while back but
couldn't locate it and am not sure it was even on RATs.

Thanks
--
Steve

Stacking the lams in in bundles of 2+2, or even 20 +20
is fiddling with the effective U of the iron
which is highest when 1+1 is used, when inductance is also highest.
If there are sufficient turns used to allow some reduction of the iron U,
and hence the primary inductance, without causing excessive phase shift and
gain loss at LF, then effectively placing a small gap in the magnetic path
and reducing U won't do much harm.
I have used a small air gap in an OPT using c-cores,
in a class A solid state amp to stop the sudden abrupt saturation which
occurred
when no gap was used.
The transformer still suffered from saturation at full power below 10 Hz,
but it wasn't as bad as with no gap.
bunching lams in an E&I tranny would have a similar effect.

To understand, you should try either way, and carefully measure what you
observe
in the LF behaviour of the tranny, in terms of unlaoded winding currents,
and distortion voltages generated at.

Patrick Turner.