[mresseguie]

FRM,

That is very helpful! Thank you 🙏.

[E55l2]

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[shooter]

I have compare regular EI core, 49%, 80% Nickel, double C core amorphous transformers in my UX250 amp, amorphous C core came in third, Nickel core not good enough? You have to listen for your self.

[E55l2]

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[shooter]

The amorphous and 80% nickel are wind specific for type 50 by the same transformer winder, the 49% is old Tango, I am not the only one that can hear the difference.

[E55l2]

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[shooter]

My amorphous core transformers are huge no problem with bass, on my friend system he prefer amorphous to nickel for his transmitter tube that’s why I said you have to listen for yourself.

[E55l2]

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[shooter]

Look up Intact Audio transformers.

[E55l2]

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[Docere]

E55l2, what you say seems to reflect my limited experience and research.

Firstly to get the Japanese transformer thing out of the way. The Japanese manufacturers, at least the three main players, measure their transformers where Zp=rp; that is, with the load is the same as a tube's plate resistance. That does not reflect a real-world situation and underestimates the capability of their transformers in use. Moreover, they tend to measure inductance at rated or maximum allowable current, which in many cases, also does not reflect real-world use - inductance will be a bit higher in practice. I suspect they do this because it facilitates apples-to-apples comparisons... but the external validity is not good (and under-estimates their real-use capability)!

How many times have I read of winders using their models and techniques developed to wind on SiFe cores using the same for amorphous cores and folks saying they sound detailed but lean? According to the winder I use, different models and techniques are required for different core materials and arrangements. Sounds believable. IME they have it right, my SET amp runs a nano-c core: it is large for the amp's output (5.5kg for about 2.5W out) and has what most would call high inductance and extended frequency range (from memory, in circuit -1dB at roughly 80kHz with smooth roll-off) - this little amp does not sound lightweight at all. Sounds lovely actually. And they have bettered that transformer design noticeably, apparently.

The way I see it, quality nano-crystalline cores are about the best there is, if they can be wound well. For my next amp I have considered a few options and will invest the $ in nano-crystalline cored transformers at input, interstage and output. Should be fun (despite bandwidth "concerns" about using so many transformers).

[E55l2]

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[Docere]

Most importent when there are datasheets published is the way how it is measured. Tango did that very good in the past, nowedays the new ISO brand is slightly less documentated.
It's not a big problem that they measured at Ra=Ri but with a lower source impedance the low frequency respons will be a bit better and high frequencies can be better but also worse (more ringing). It will help to do more measurements with real tubes.
The measured inductance at rated anode current is good, better is possible but that is not specially needed if the differance between the rated and real anode current is not to big. If it is big then probably you using the wrong transformer anyway.

Some things never change, you can calculate with the same formulas any transformer. Just use the right parameters. If a winder has problems then the winder already has the wrong model or technique in the first place.

I fully agree about your comment about nanocrystalline material/transformers.
A decent 1:1 interstage with nano core can cost less then $300

I don't know what kind of input transformer you want but with a step-up could be tricky (unless the source impedance is very low)
A 1:1 interstage has normally an extreme wide bandwith. Mostly the output transformer is the limited but if you have tubes with a high Ri then the tubes will set for the limit too.

Thanks E55l2.  The step-up is relatively small at 1:2.5. The source impedance is lower than the rp of the input/driver tube, which is why I put the step-up at the input rather than interstage (which also needs to handle up to 30mA current). Hopefully my thinking is okay.

[SET Man]

Hey!

    Hmmm... I must say that I find the discussion between different transformer types here interesting and informative. Well, thanks guys.

   As for my transformers. I bought my Welborne Labs Apollo SET back in 1999 and both main power and output transformer, all EI type are made by Electra Print.

Buddy

[FullRangeMan]

Hi E55L2,
Read your post on EI lamination I always wondered how good are the GOSS.
They are really oriented?

[E55l2]

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[Unison845]

This is what TANGO X10S core look like before being potted.

[E55l2]

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[E55l2]

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[FullRangeMan]

E55L2,
What is this transformer?
EI, C core, choke ?