GroupDIY
Project Specific Discussions => Magnetics => Topic started by: mjrippe on March 31, 2020, 03:07:42 PM

Picked this one up and found little info about it. Internet claims it is an input like the XT2 and XT3. My thinking is that it's an output, due to larger size and knowing how they did things back then. Photographed with my measurements and an XT3 for size reference.

Hmm. 19 as same winding is unusual labeling.
414DCR definitely doesn't look like 60K at a glance.

Yeah, 19 is same as the XT2 and 3 but an odd choice for sure. The 60k was from some internet dude who was probably quoting the XT2 spec and ASSuming the 10 was the same. Like I said, I suspect it is an OPT so more like 10k.

What’s the turns ratio?

What’s the turns ratio?
From the 12.7mH of the 50 ohm winding and the 102H of the secondary the inductance ratio is about 8500 to 1 so the turn ratio is the square root of this which is close to 92:1. If the 12.7mH primary is indeed 50 ohms them reflected to the secondary it is about 47K which is not oo far from 60K.
In conclusion I think it is most likely an input transformer. It is perhaps bigger than expected because they must have used thicker the usual wire for the secondary to keep the dcr down.
Cheers
Ian

Ugh, my bad folks. Mislabeled that measurement as pin 8 to pin 5, it was actually 83. Here is a fresh pic with measurements of all windings. No 60Hz measurement on the secondary because my Sencore does not go over 10H.

So following Ian's math, I get 8024:1 ratio. Square root is 89.6. I am guessing a 600 ohm winding, so 53.7k Ohms. Looks like input after all!

The primary dcrs and inductances don't seem to match up. You would expect greatest dcr to correspond with greatest dcr but they do not.
Cheers
Ian

The primary dcrs and inductances don't seem to match up. You would expect greatest dcr to correspond with greatest dcr but they do not.
and 414 ohms seems way low for a ~60k nominal secondary. Would normally expect something in the mid thousands, typically around 3.5k  6.5k

and 414 ohms seems way low for a ~60k nominal secondary. Would normally expect something in the mid thousands, typically around 3.5k  6.5k
If you take the 154mH as the 300 ohm winding and the secondary inductance as 102H then the impedance ratio is about 662 so the secondary impedance would be closer to 20K than 60K and the ratio not far from 25:1.
Cheers
ian

and 414 ohms seems way low for a ~60k nominal secondary. Would normally expect something in the mid thousands, typically around 3.5k  6.5k
Again, yeah. More likely to see in a modern transformer versus an old one, but still rare. I'm usually suspicious if I see less than 1K5, what with the usual (PRR) rule of roughly 10% for DCR versus Ω.
Bench test for level into a hiZ DI would be my next test, see what it really delivers, out versus in.
Then there's the other direction seen in some Western Electric, Langevin, and RCA, of really high DCR, like up to 75% of rated Ω. I still haven't found anything informative about that design decision.

Yeah, Doug. 1.5k is a better ballpark reference for the lower end of the DCR range.
For reference, I pulled a few off the shelf that were in easy reach in the closet. All mic or line to grid:
Newcomb TR100: _________________________________________3.199k ohms
UTC P16 (O1):____________________________________________ 1.989k ohms
Thordarson T50644 (K7120744) from GE 4BA1F: _____6.471k ohms
Triad 2426 (custom unit from the 50s or 60s): ____________5.932k ohms
Chicago BI1: _______________________________________________1.343k ohms
RCA XT2746 from BA2A: ________________________________4.631k ohms
RCA XT2874A from BA3C:______________________________ 2.936k ohms

The primary dcrs and inductances don't seem to match up. You would expect greatest dcr to correspond with greatest dcr but they do not.
Cheers
Ian
I know you meant dcrinductance there, and that confused me as well. Maybe I am mismeasuring something. Maybe I should send it to CJ! Where is he lately?