I cheated a little bit. Remember, I have a 7903 right here on the bench.
I thought that the goofy level readings around 15 hertz on Brand B were something wrong with your tests, but when I put my 7903 on the scope and saw that instability on the low end with a square wave and 600 ohm load, I knew I had one choice down, as low end instability is pretty rare among transformers.
Also, thats a mic input being used as an output, so I figured that the winding structure might not be the best for an output transformer.
So then I was down to a fifty/fifty chance. I figured that Sowter had about 40 more years on UTC as far as technology is concearned, and that their transformers seem to work well as a group, so that led me to believe that the better curves belonged to them. I also looked at their data sheets. They have a big EI framed core with 50 percent silicon, so I figured that their core would be the strongest as far as low frequency vs loading is concerned. The loading curves helped a lot because you were only loading the output iron.
I also know that Sowter tilts their response towards the high end a bit more than UTC from listening tests. This is probably due to the small high Ni core, where as UTC has always been great from 20 hertz on down, and sure enough, if you look at the low end distortion specs, UTC actually beats out Sowter at 10 hertz. This would be the bigger UTC input core taking over.
But I don't know. You could come back and tell me that you made a mistake and that the order is backwards, and I could probably find new reasons to make that plan fit. Why? Becuase transformers are weirder than I am.
If you guys are still set up, I would love to see that distortion vs level chart done at a low freq, like 50 or 20 hz.
And thanks for this cool test!!!
:thumb:
I thought that the goofy level readings around 15 hertz on Brand B were something wrong with your tests, but when I put my 7903 on the scope and saw that instability on the low end with a square wave and 600 ohm load, I knew I had one choice down, as low end instability is pretty rare among transformers.
Also, thats a mic input being used as an output, so I figured that the winding structure might not be the best for an output transformer.
So then I was down to a fifty/fifty chance. I figured that Sowter had about 40 more years on UTC as far as technology is concearned, and that their transformers seem to work well as a group, so that led me to believe that the better curves belonged to them. I also looked at their data sheets. They have a big EI framed core with 50 percent silicon, so I figured that their core would be the strongest as far as low frequency vs loading is concerned. The loading curves helped a lot because you were only loading the output iron.
I also know that Sowter tilts their response towards the high end a bit more than UTC from listening tests. This is probably due to the small high Ni core, where as UTC has always been great from 20 hertz on down, and sure enough, if you look at the low end distortion specs, UTC actually beats out Sowter at 10 hertz. This would be the bigger UTC input core taking over.
But I don't know. You could come back and tell me that you made a mistake and that the order is backwards, and I could probably find new reasons to make that plan fit. Why? Becuase transformers are weirder than I am.
If you guys are still set up, I would love to see that distortion vs level chart done at a low freq, like 50 or 20 hz.
And thanks for this cool test!!!
:thumb: