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Original Message

RE: Ignore the doubters!

Posted by mqracing on September 21, 2015 at 14:06:42:

many of the "coveted" WE audio transformers such as the 171A output trans the core was a C and I configuration (both the C and I being stamped from 26 guage (.0185") M19 material. The two c's are closed around the I which is located in the middle.

The C and I arrangement is not very efficient from the vantage point of having many gaps of high reluctance.

M19 has triple the core losses than M6 and just a fraction of M6's superior (i.e., greter) permeability. And has less power handling capacity to boot.

That same 171A coil wrapped in a modern core (such as M6 or better) will have much better performance specs.

Two other quick thoughts. You mentioned "thin" lams... you can get M6 stamped from. 006" material... though as with all of the thinner core materials the penalty is having a poorer stacking factor... so that, in practice, you've reduced the core cross section area... which raises the flux density (and by extension reduces power handling). I don't see it as being advantageous in audio transformer designs.

A point to consider as regards c cores is that they tend to have large (uninterrupted) air gaps versus an interleaved EI core. Take the same transformer and build one with EI's and one with c-cores (using the same grade of lam)... then measure the no load exciting current for each... and tell me what you've discovered.

I fail to see any magic in c-cores and whenever possible will build with an EI (or other stamped lam shape) which can be assembled and fitted by hand stacking for an optimum fit with the wound coil.

MSL