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In Reply to: RE: Ignore the doubters! posted by dave slagle on September 21, 2015 at 07:26:02
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
Builder of MagneQuest & Peerless transformers since 1989
Edits: 09/21/15 09/21/15 09/21/15 09/21/15 09/21/15Follow Ups:
Hello, Mikey and Dave.I used to service nearly all W.E. stuff. I serviced Movie Theatres, and later bought and built theatres of my own, and also built stadium-type theatres for new owners.
W.E. gear I ran into a lot. At first, when servicing an older theatre, I would remove the W.E. model 91A amps, or some of their bogus attempts at making push-pull amps, remove the speakers and their drivers, give the junk away and replace the amps with McIntosh MC-60's (which I lightly modded), and the speakers with clean, sonically and directionally ACCURATE units such as ALTEC or JBL.
Later on, the Japanese went bonkers over historic W.E. gear, and we saved the old junk and sold it to them-- we sure didn't like to listen to it.. Interestingly, MGM pictures boycotted ALL W.E. gear in their theatres because it totally butchered the "live", accurate, sonic presence that MGM wanted for their theatres. I believe a Mr. Jim Lansing was hired to design something better, and he surely did!
The point of this is that I got better sound-- a lot better-- without the W.E. gear. Today, one can also get better sound by avoiding the misdesigned 300B tube, unless it is one that is made symmetrically with vertical filament structures by EML, etc.
Love you guys, keep up the good work!
---Dennis---
Edits: 10/08/15
hey... just to have some fun here...
That same 171A coil wrapped in a modern core (such as M6 or better) will have much better performance specs.
by what definition of performance?
Re thin lams....I have some .006" thick nickel and it is fragile as hell but with C-cores even .001 is rigid. I'm not making a judgement just noting differences between the stamped vs. tape wound topologies. I typically use non-oriented materials and tend toward stamped laminations where the only two main differences between the cut core and stamped lamination are lam thickness and gap size. I'm not saying thinner lams are better... just making the observation and in the case of amorphous material which is .001" thick, a c-core is the only option.
Now when we move onto gap size, the Cut cores have two discrete gaps that cover the area of the core. This means that the smallest gap possible depends on the finish of the mating surface. A while back there was a company offeing cut tape wound cores with a stepped surface to increase the surface area of the gap which makes it effectively smaller. With stamped laminations you have the option of alternately stacking the laminations which greatly increases the surface area of the gap making far smaller gaps possible than with cut cores. So to answer your question... for a given coil and core geometry a power transformer stacked with 1X1 EI laminations will have far less magnetizing current than a pair of C-cores in a shell configuration since the stamped laminations allow for a much smaller effective gap.
For years people have asked me to use 80% nickel C-cores for my autoformer since 'C-cores are better'. I try to explain that if I were to move to a cut core I would end up with a maximum of 1/10th the possible inductance of a 1X1 stacked EI configurtation. If all your sources are 50 ohms then it isn't an issue but in the real world we need to do some pretty nasty stuff to meet that goal so I opt for the EI lams as the best option.
dave
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